Posts Tagged ‘Chronic myelogenous leukemia’

New PCR Based Test May be Able to Detect Low Levels of Persistent CML, Guiding TKI therapy Choices

from Novel Assay Could Help Guide Treatment Cessation Decisions in CML

Reporter: Stephen J. Williams, Ph.D.

News | February 15, 2016 | Chronic Myeloid Leukemia, Hematologic Malignancies, Leukemia & Lymphoma
By Dave Levitan
A new personalized DNA-based assay can detect very low levels of persistent disease in chronic myeloid leukemia (CML) patients thought to be in deep remission, according to a new study. The test could help with treatment choices regarding cessation of tyrosine kinase inhibitor (TKI) therapy in these patients.
A number of recent studies have examined the possibility that some patients could stop TKI therapy after achieving deep molecular remission. “However, the safe introduction of a TKI-withdrawal strategy would require a reliable and cost-effective method for the identification of those patients with the lowest likelihood of relapse,” wrote study authors led by Alistair G. Reid, BSc, PhD, of Imperial College London.

Because the likelihood of relapse after withdrawal from therapy is probably related to persistence of residual disease, testing for low levels of BCR-ABL1–positive disease is key. In the new study, the researchers tested an assay using personalized DNA-based polymerase chain reaction (dPCR) involving identification of t(9;22) fusion junctions. The results were published in the Journal of Molecular Diagnostics.

They successfully mapped genomic breakpoints in 32 of 32 samples from CML patients with early-stage disease. Next, they tested 46 samples from 6 patients following treatment with a TKI and compared results to other quantitative PCR methods; 10 of the samples were used as positive controls, while the others were considered to be in deep molecular remission.

Of those 36 samples, dPCR detected persistent disease in 81%. This was more sensitive than two other PCR-based approaches, including RT-dPCR (25%) and DNA-based quantitative PCR (19%).

“The technologies described allow for the assignment of absolute quantities to both BCR-ABL1 DNA and RNA targets, facilitating for the first time direct comparison of mean expression vs cellular disease burden,” the authors wrote. They added that it remains to be explored whether the risk of relapse after withdrawal of therapy is related to just the number of CML cells or also to the degree of transcriptional activity in those cells.

“If validated in clinical trials of stopping TKIs, this technique will permit a more personalized approach to recommendations for dose reduction or drug cessation in individual patients, ensuring that therapy is withdrawn only from patients with the highest chance of long-term remission,” said study author Jane F. Apperley, MD, PhD, also of Imperial College London, in a press release. “The technique we describe, with which we successfully mapped a disease-specific junction in all patients tested, is relatively simple, cost-effective, and suited to a high-throughput laboratory.”

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 Update on Chronic Myeloid Leukemia

Curator: Larry H Bernstein, MD, FCAP


Diagnosis and Treatment of Chronic Myeloid Leukemia in 2015
Philip A. Thompson, Hagop M. Kantarjian, Jorge E. Cortes,
Department of Leukemia, The University of Texas, MD Anderson Cancer Center, Houston

Target Audience: The target audience for Mayo Clinic Proceedings is primarily internal medicine physicians and other clinicians who wish to advance their current knowledge of clinical medicine and who wish to stay abreast of advances in medical research.
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Learning Objectives: On completion of this article, you should be able to (1) identify clinical and laboratory features consistent with a diagnosis of chronic myeloid leukemia (CML) and diagnose the disease based on laboratory testing; (2) identify factors associated with poor treatment outcomes and how these are identified and managed; and (3) describe standard first and second line therapeutic options for CML and their adverse effects.
In their editorial and administrative roles, William L. Lanier, Jr, MD, Terry L. Jopke, Kimberly D. Sankey, and Nicki M. Smith, MPA, have control of the content of this program but have no relevant financial relationship(s) with industry.
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Article Outline
I. Clinical Features
A. Presenting Hematologic Parameters
II. Differential Diagnosis
A. Chronic Myelomonocytic Leukemia
B. Atypical CML
C. Chronic Neutrophilic Leukemia
D. Essential Thrombocythemia
E. Diagnostic Workup
III. Determining Prognosis in CP-CML at Baseline
IV. Response Definitions
V. Routine Monitoring Schedule
VI. Initial Treatment of CP-CML
A. Which TKI and Dose?
VII. Treatment Objectives
A. Achievement of CCyR and MMR/MR3.0
B. Definitions of Treatment Failure
VIII. Treatment of Patients With Primary or Secondary Treatment Failure Who Remain in CP
A. Switching to a Second TKI
IX. Stopping Treatment in Patients With Prolonged CMR
X. Treatment of AP-CML
XI. Treatment of BP-CML
A. Treatment of LBP
B. Treatment of MBP
C. Which TKI Should Be Used in BP-CML?
D. Treatment of Refractory and Relapsed BP
XII. Conclusion
XIII. References

Few neoplastic diseases have undergone a transformation in a relatively short period like chronic myeloid leukemia (CML) has in the last few years. In 1960, CML was the first cancer in which a unique chromosomal abnormality was identified and a pathophysiologic correlation suggested. Landmark work followed, recognizing the underlying translocation between chromosomes 9 and 22 that gave rise to this abnormality and, shortly afterward, the specific genes involved and the pathophysiologic implications of this novel rearrangement. Fast forward a few years and this knowledge has given us the most remarkable example of a specific therapy that targets the dysregulated kinase activity represented by this molecular change. The broad use of tyrosine kinase inhibitors has resulted in an improvement in the overall survival to the point where the life expectancy of patients today is nearly equal to that of the general population. Still, there are challenges and unanswered questions that define the reasons why the progress still escapes many patients, and the details that separate patients from ultimate cure. In this article, we review our current understanding of CML in 2015, present recommendations for optimal management, and discuss the unanswered questions and what could be done to answer them in the near future.
Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm, characterized by the unrestrained expansion of pluripotent bone marrow stem cells.1 The hallmark of the disease is the presence of a reciprocal t(9;22)(q34;q11.2), resulting in a derivative 9q+ and a small 22q−. The latter, known as the Philadelphia (Ph) chromosome, results in a BCR-ABL fusion gene and production of a BCR-ABL fusion protein2; BCR-ABL has constitutive tyrosine kinase activity3 and is necessary and sufficient for production of the disease.4 In a few cases (5%-10%), the Ph chromosome is cytogenetically cryptic, often due to a complex translocation, and the diagnosis requires fluorescence in situ hybridization (FISH) to reveal the BCR-ABL fusion gene or polymerase chain reaction (PCR) to reveal the BCR-ABL messenger RNA transcript.5 A 210-kDa BCR-ABL transcript (p210) transcribed from the most common rearrangements between exons 13 or 14 of BCR and exon 2 of ABL (known as e13a2 [or b2a2] and e14a2 [or b3a2], respectively) is most common, but rare cases will have alternative BCR-ABL breakpoints, leading to a p190 transcript (from the e1a2 rearrangement, most typically seen in Ph-positive acute lymphoblastic leukemia [ALL]) or a p230 transcript.5 Indication of the typical hematopathologic features and the t(9;22)(q34;q11.2) by conventional cytogenetics or FISH and/or BCR-ABL by PCR is required for diagnosis.5

Clinical Features
Up to 50% of patients are asymptomatic and have their disease diagnosed incidentally after routine laboratory evaluation.6 Clinical features, when present, are generally nonspecific. Splenomegaly is present in 46% to 76%6, 7 and may cause left upper quadrant pain or early satiety, fatigue, night sweats, symptoms of anemia, and bleeding due to platelet dysfunction may occur, the last occurring most commonly in patients with marked thrombocytosis. Less than 5% of patients present with symptoms of hyperviscosity, including priapism, which are generally seen when the presenting white cell count exceeds 250,000/μL.7
The disease is classically staged into chronic phase (CP, most patients at presentation), accelerated phase (AP), and blast phase (BP).5 Many definitions have been used for these stages, but all the data generated from the tyrosine kinase inhibitor (TKI) studies have used the historically standard definition in which AP is defined by the presence of one or more of the following: 15% or more blasts in peripheral blood and bone marrow, 20% or more basophils in peripheral blood, and platelet counts less than 100,000/μL unrelated to treatment or the development of cytogenetic evolution. The blast phase is defined by the presence of 30% or more blasts in the peripheral blood or bone marrow, the presence of clusters of blasts in marrow, or the presence of extramedullary disease with immature cells (ie, a myeloid sarcoma).8 Progression to BP occurs at a median of 3 to 5 years from diagnosis in untreated patients, with or without an intervening identifiable AP.6

Presenting Hematologic Parameters
Characteristic complete blood cell count features are as follows: absolute leukocytosis (median leukocyte count of 100,000/μL) with a left shift and classic “myelocyte bulge” (more myelocytes than the more mature metamyelocytes seen on the blood smear); usual blast counts of less than 2%; nearly universal absolute basophilia, with absolute eosinophilia in 90% of cases5; monocytosis but generally not an increased monocyte percentage; absolute monocytosis in the unusual cases with a p190 BCR-ABL9; normal or elevated platelet count; and thrombocytopenia, which suggests an alternative diagnosis or the presence of AP, rather than CP, disease.

Differential Diagnosis
The differential diagnosis for chronic phase CML (CP-CML) includes the following Ph-negative conditions.

Chronic Myelomonocytic Leukemia
Chronic myelomonocytic leukemia is a myelodysplastic/myeloproliferative neoplasm that can be distinguished from CML by the presence of dysplastic features, more prominent cytopenias, more prominent monocytosis, and lack of basophilia. Chronic myelomonocytic leukemia is Ph negative and may have other cytogenetic abnormalities.5

Atypical CML
Atypical CML is a Ph-negative myelodysplastic/myeloproliferative neoplasm.

Chronic Neutrophilic Leukemia
Rare cases of CML with a p230 BCR-ABL transcript may be mistaken for chronic neutrophil leukemia (CNL) because of the predominant neutrophilia associated with this version of CML, but cytogenetics revealing the Ph chromosome will easily distinguish them. Importantly, this and other atypical rearrangements might not be detected by some standard PCR methods. The presence of these abnormalities should be suspected in instances where the Ph chromosome is detected by routine karyotype but with PCR “negative” for BCR-ABL, hence the importance of cytogenetic evaluation in all patients at baseline.

Essential Thrombocythemia
Rare cases of CML may present with isolated thrombocytosis, without leukocytosis. Basophilia is often present as a diagnostic clue. These cases will be distinguished by cytogenetics and molecular studies revealing Ph positivity and BCR-ABL positivity.10

Diagnostic Workup
The diagnosis will usually be suspected from the complete blood cell count and blood smear. FISH for t(9;22)(q34;q11.2) and quantitative reverse transcriptase PCR (qRT-PCR) for BCR-ABL can be performed on peripheral blood. However, bone marrow aspirate and unilateral biopsy with conventional cytogenetics and flow cytometry are essential at the time of diagnosis to exclude unrecognized advanced-stage disease and to detect rare cases with an alternative BCR-ABL transcript not detected by routine BCR-ABL PCR. Flow cytometry will identify cases with unrecognized progression to lymphoid blast crisis by their phenotypic features, whereas conventional karyotyping may identify additional cytogenetic abnormalities (cytogenetic clonal evolution).

Determining Prognosis in CP-CML at Baseline
The prognosis of CP-CML has markedly improved since the development of TKIs. The stage of disease is the most important prognostic feature. Most patients presenting with CP-CML achieve long-term control, and stem cell transplant is only needed in a few. Several prognostic scoring systems have been developed to assess the risk of poor outcome at presentation: the Sokal score11 and Hasford score were developed in the pre-imatinib era12 but retain prognostic significance in imatinib-treated patients. An online calculator is available to compute both these scores at Approximately 25% of high-risk patients fail to achieve complete cytogenetic response (CCyR) with imatinib-based treatment by 18 months; this and other important therapeutic milestones are discussed in detail subsequently. A simpler system based on basophil percentage in peripheral blood and spleen size, the European Treatment and Outcome Study (EUTOS) system, found that 34% of high-risk patients fail to achieve CCyR by 18 months.13Notwithstanding the appeal of the simplicity of the EUTOS score, its predictive value has not been universally confirmed.14, 15 The prognostic relevance of these classifications is ameliorated but not completely eliminated among patients treated with second-generation TKIs. Currently, we do not make treatment decisions based solely on these risk scores.
Other proposed pretreatment predictors include the level of CML cell membrane expression of the organic cation transporter-1 (OCT-1). OCT-1 is required for entry of imatinib into the cell; this protein (and its corresponding RNA) can be measured, and higher levels of expression and/or activity are associated with superior survival in imatinib-treated patients.16 Importantly, patients with lesser OCT-1 activity may benefit more from higher starting doses of imatinib.16 OCT-1 activity is not important for nilotinib-17 or dasatinib-treated patients because these drugs are not OCT-1 substrates.18

Response Definitions
Dynamic response assessment is essential to identify patients at high risk of disease progression, who may benefit from a change of therapy. Response definitions are given in Table 1.19 A complete hematologic response (CHR) is defined by clinical and peripheral blood criteria. Cytogenetic response is classified according to the percentage of Ph-positive metaphases by routine karyotype on bone marrow aspiration. A CCyR has also been defined in some instances by interphase FISH on peripheral blood as the absence of detectable BCR-ABL fusion in at least 200 examined nuclei.20 Molecular testing for BCR-ABL transcripts using qRT-PCR is more sensitive for low-level residual disease than cytogenetics or FISH (sensitivity of 10−4 to 10−5). Levels of response in this qRT-PCR assay are clinically relevant and reported as a percentage of the transcript levels of a normal housekeeper gene, such as ABL1 or BCR. Given that assays used by different laboratories have significantly different sensitivities, attempts have been made to harmonize reporting by developing the international scale. By parallel testing of samples with a reference laboratory, laboratory-specific conversion factors are produced to correct for differing sensitivities and allow a laboratory to report BCR-ABL transcript levels in a more uniform way.21 A World Health Organization standard material has also been developed for assay calibration.22 Major molecular response (MMR or MR3.0) corresponds to less than 0.1% BCR-ABL on the international scale, which represents a 3-log reduction from the standardized baseline rather than a 3-log reduction from the individual patient’s baseline BCR-ABL transcript level (which can vary significantly).23 MR4.0is less than 0.01% bcr-abl on the international scale, and MR4.5 is 0.0032% or less on the international squale (equivalent to a ≥4.5-log reduction), which is the limit of sensitivity of many assays. There is also a fair correlation between transcript levels and depth of cytogenetic response such that transcript levels of 1% on the international scale are grossly equivalent to a CCyR.
Table 1Definitions of Response
Response Definition
CHR Leukocyte count <10 × 109/L, basophils <5%, platelets <450 × 109/L, the absence of immature granulocytes, impalpable spleen
Minor CyR 36%-95% Ph+ metaphases in bone marrow
Major CyR 1%-35% Ph+ metaphases in bone marrow
CCyR 0% Ph+ metaphases in bone marrow
MMR BCR-ABL International Scale ≤0.1%
CMR Undetectable BCR-ABL with assay sensitivity ≥4.5 or 5.0 logs
CHR = complete hematologic response; CMR = complete molecular response; CyR = cytogenetic response; MMR = major molecular response; Ph = Philadelphia chromosome.

Routine Monitoring Schedule
Different monitoring schedules have been proposed, with the aim of early identification of patients who are not achieving therapeutic milestones and are therefore at higher risk of disease progression. Our own practice is to monitor the complete blood cell count every 1 to 2 weeks for the first 2 to 3 months to identify treatment-related cytopenias and the achievement of complete hematologic response. Most instances of grade 3 to 4 myelosuppression occur in the first few months. Thus, once the peripheral blood cell counts become stable, monitoring with complete blood cell count can be reduced to every 4 to 6 weeks and eventually every 3 to 6 months. In addition, BCR-ABL qRT-PCR is performed from peripheral blood every 3 months until the achievement of MMR then every 6 months thereafter. We perform a bone marrow aspiration with cytogenetics every 6 months until achievement of stable CCyR. This allows not only for the confirmation of CCyR but also for the discovery of chromosomal abnormalities in the emerging Ph-negative metaphases, a phenomenon that occurs in 10% to 15% of patients and may be associated with eventual development of myelodysplastic syndrome or acute myeloid leukemia.24, 25, 26 Subsequently, bone marrow examination only need be performed in the following circumstances: failure to achieve therapeutic milestones; evaluation of a significant, unexplained increase in BCR-ABL after initial response, not attributable to lack of adherence (see later sections for evaluation of suboptimal response or loss of response); to monitor known chromosomal abnormalities in Ph-negative metaphases; and to investigate unexplained cytopenia(s).

Initial Treatment of CP-CML
The TKIs have transformed outcomes in CML. The pivotal International Randomized Study of Interferon and STI571 (IRIS) study found far superior rates of CHR, CCyR, and MMR in imatinib- compared with interferon-treated patients and a superior progression-free survival (PFS).27, 28 Before IRIS, other than interferon-based therapy, allogeneic stem cell transplant (alloSCT) was the treatment of choice for eligible patients and achieved long-term disease-free survival (DFS) in approximately 50% to 85% of patients29, 30, 31, 32, 33 due to a graft-vs-leukemia effect.34 AlloSCT is associated with a unique toxicity profile, particularly opportunistic infections and graft-vs-host disease, resulting in treatment-related mortality of 5% to 20% and significant morbidity in many long-term survivors. Combined with the marked success of TKIs, alloSCT is now reserved for patients with advanced-stage disease or treatment failure; this is discussed in more detail in later sections.

Which TKI and Dose?
Three TKIs are now approved by the Food and Drug Administration for initial treatment of CP-CML: imatinib, nilotinib and dasatinib. Debate continues regarding the optimal initial TKI and dose, with compelling arguments supporting each. A number of studies have attempted to improve on results achieved with 400 mg/d of imatinib.
Shortly after imatinib was introduced as frontline therapy for CML, studies focused on use of higher doses to improve outcome.35 The single-arm TIDEL (Therapeutic Intensification in De Novo Leukemia) study, in which patients were treated with 600 mg/d of imatinib, found superior rates of MMR at 12 and 24 months in those patients able to maintain a daily mean of 600 mg of imatinib for the first 6 months36; in our experience, 400 mg of imatinib twice daily was associated with superior cumulative rates of CCyR and MMR relative to a historical control cohort and was generally well tolerated, with 82% of patients continuing to take at least 600 mg/d.37, 38In a confirmatory randomized study, the German CML study group reported that an initial imatinib dose of 800 mg was associated with higher rates of MMR at 12 months than 400 mg of imatinib or 400 mg of imatinib plus interferon alfa (59% vs 44% vs 46%). The mean daily dose tolerated in the group assigned to 800 mg of imatinib was 628 mg because of the higher adverse event profile of higher doses.39 The higher initial dose was also associated with more rapid achievement of MR4.5. There was, however, no event-free survival (EFS) or survival benefit, relative to 400 mg/d of imatinib.
Combinations of imatinib and interferon have been reported in several randomized trials, with mixed results. The French SPIRIT (STI571 Prospective International Randomized Trial) study and a Nordic group found higher rates of MMR at 12 months for patients receiving imatinib plus pegylated interferon alfa 2a or pegylated interferon alfa 2b, respectively, but no difference in CCyR.40, 41 In contrast, the German CML study group found no difference in MMR at 12 months between 400 mg of imatinib with or without nonpegylated interferon alfa,39and there was no difference in the rates of CCyR or MMR when pegylated interferon alfa 2b was combined with 800 mg/d of imatinib compared with imatinib alone.42 All studies have found poor tolerability of interferons with high rates of discontinuation, and none have found PFS or survival benefit.
Ten years ago, the first studies using second-generation TKI as initial therapy for CML were initiated, which found very high rates of CCyR and MMR using first-line dasatinib, 100 mg/d or 50 mg twice daily,43 and nilotinib, 400 mg twice daily.44, 45 Two major company-sponsored randomized studies later confirmed these results, comparing second-generation TKIs to imatinib, 400 mg/d. The Evaluating Nilotinib Efficacy and Safety in Clinical Trials-Newly Diagnosed Patients study (ENEST-nd) compared imatinib, 400 mg, to nilotinib, 300 mg, twice daily and nilotinib, 400 mg, twice daily. Nilotinib at both doses was associated with more, faster, and deeper responses and higher freedom from progression. The 400-mg twice-daily dose was associated with a small, but statistically significant, improvement in overall survival (OS) compared with 400 mg of imatinib; however, the results were also notable for a significantly higher incidence of major arteriothrombotic events, including ischemic heart disease, cerebrovascular accidents, and peripheral arterial disease (especially at 400 mg twice daily).46 The Dasatinib versus Imatinib Study in Treatment-Naive CML Patients (DASASION) compared 400 mg/d of imatinib with 100 mg/d of dasatinib. More, faster, and deeper responses were seen, with fewer transformations to AP and BP, but at 5 years of follow-up (the end of the study), there was still no PFS or OS benefit.47 A frequent (although usually grade 1 or 2) adverse effect of dasatinib is the development of pleural effusions, which may require dose adjustments and occasionally thoracentesis. Of some concern, also, was the development of pulmonary hypertension, which was diagnosed in 8 patients by echocardiographic criteria; however, only one patient had right-heart catheterization, which did not confirm pulmonary hypertension.
Imatinib, 400 mg, has also been compared with bosutinib, 500 mg. Faster and deeper responses, with a higher rate of MMR (but not CCyR, the primary end point) at 12 months, were seen in the bosutinib group, leading to fewer transformations. There was a higher rate of treatment discontinuation in the bosutinib arm, particularly due to diarrhea and liver function test abnormalities.48 A second randomized trial, using a lower starting dose of bosutinib (400 mg/d), has been initiated, seeking regulatory approval for this indication.
Ponatinib is a highly potent TKI and is the only TKI with activity in patients with the T315I mutation in ABL1. Because of the high level of preclinical and clinical activity of ponatinib in the salvage setting,49 it was also investigated as frontline therapy. Both a single-arm, phase 2 study50 and a randomized phase 3 study were conducted, the latter comparing 400 mg of imatinib with 45 mg of ponatinib.51 Ponatinib treatment resulted in faster and deeper responses, including very high rates of early MR4.5. Both studies reported a 3-month rate of BCR-ABL/ABL less than 10% of 94%, the highest of any study with TKI. Unfortunately, the high rate of major arterial thrombotic events (7% in the ponatinib arm vs 1% in the imatinib arm) and pancreatitis led to the 2 studies being terminated early at a median follow-up of 23 and 5.1 months, respectively.51
We believe that imatinib, dasatinib, and nilotinib all constitute adequate treatment options for patients with CML at the time of diagnosis. Outside clinical trials, the decision regarding which TKI to use should be tailored to an individual patient and depends on an assessment of factors such as the relative risk of the disease, risk factors for specific adverse events (eg, arteriothrombotic events, pleural effusion, pulmonary hypertension, poorly controlled diabetes, and pancreatitis), possible effect of the dose administration schedule, and cost. In patients with a poorer likelihood of responding to 400 mg of imatinib (eg, those with high Sokal scores or those with e1a2 CML), a second-generation TKI might be preferred. Patients with low OCT-1 activity may also benefit from high-dose imatinib or a second-generation TKI, but this test is not clinically available in the United States. In contrast, in patients with lower-risk disease or those with a higher risk for arteriothrombotic events, imatinib might be preferred. Higher doses of imatinib might offer similar efficacy benefits as dasatinib or nilotinib (eg, similar rates of early responses and transformation to AP and BP).50 Although higher-dose imatinib is associated with increased incidence of some adverse events, these usually consist of peripheral edema, muscle cramps, and gastrointestinal toxicity, but not arteriothrombotic events. Specific agents may be avoided because of their particular toxicity profiles; for example, it may be preferable not to use nilotinib in a patient with a history of coronary artery disease or with several coronary risk factors, and dasatinib may be avoided in patients who have tenuous respiratory function because of the risk of pleural effusions. Increasingly, pharmacoeconomic concerns may drive therapeutic decision making; generic imatinib will soon be available, and there will be a substantial cost differential between imatinib and second-generation TKIs, which no doubt will be a factor in the decision-making process.

Treatment Objectives
Response definitions according to hematologic, cytogenetic, and molecular criteria are given in Table 1.19, 52 It is important to remember that different laboratories have different BCR-ABL qRT-PCR sensitivity, and quantitative results may differ markedly.53 If the laboratory does not report results on the international scale, BCR-ABL should be monitored in the same laboratory for consistency. In addition, MMR cannot be adequately identified if a laboratory does not report on the international scale, increasing the importance of cytogenetic analysis for response assessment.

Achievement of CCyR and MMR/MR3.0
The European LeukemiaNet (ELN) 2013 guidelines (Table 2) place a strong emphasis on the importance of achieving MMR, ideally by the 12-month time point. This is achieved by 1 year in 18% to 58% of patients taking 400 mg of imatinib and 43% to 77% taking 600 to 800 mg.19 This is based on data from long-term follow-up of IRIS,54 which found that, of patients in MMR at 18 months, only 3% lost CCyR, compared with 26% of patients with BCR-ABL levels of greater than 0.1% to less than 1.0%. The key transcript levels at the 6-, 12-, and 18-month landmarks found to be associated with favorable EFS were 10% or less, 1% or less, and 0.1% or less, respectively.54, 55 Despite the importance of achieving MMR with imatinib, however, there are no data to indicate that switching therapy in a patient in the ELN warning (formerly suboptimal response) category improves outcome.56 In addition, our own data suggest that achievement of MMR offers no EFS or survival advantage over the achievement of CCyR by 12 or 18 months during frontline treatment with second-generation TKIs; achievement of CCyR by 3 months should be considered optimal response in this setting, with PCyR considered suboptimal.57 In a combined analysis of patients receiving either imatinib or second-generation TKIs, patients achieving CCyR by 6 months have a 97% 3-year EFS on landmark analysis, which was the major point of difference, and this did not differ according to subsequent achievement of MMR or not.58
Table 2European LeukemiaNet (ELN) Response Criteriaa
Optimal Warning Failure
Baseline NA High risk or CCA/Ph+, major route NA
3 mo BCR-ABL1 ≤10% and/or Ph+ ≤35% BCR-ABL1 >10% and/or Ph+ 36%-95% Non-CHR and/or Ph+ >95%
6 mo BCR-ABL1 <1% and/or Ph+ 0 BCR-ABL1 1%-0% and/or Ph+ 1%-35% BCR-ABL1 >10% and/or Ph+ >35%
12 mo BCR-ABL1 ≤0.1% (ie, MMR) BCR-ABL1 >0.1%-1% (ie, lack of MMR) BCR-ABL1 >1% and/or Ph+ >0% (ie, lack of CCyR)
Then and at any time BCR-ABL1 ≤0.1% CCA/Ph− (−7, or 7q−) Loss of CHR

Loss of CCyR

Confirmed loss of MMRb


aCCA/Ph+ = clonal cytogenetic abnormalities in Ph-positive cells; CCA/Ph− = clonal cytogenetic abnormalities in Ph-negative cells; CCyR = complete cytogenetic response; MMR = major molecular response; NA = not applicable; Ph = Philadelphia chromosome.
bIn 2 consecutive tests, at least one of which has BCR-ABL transcripts of 1% or greater.
Several studies38, 47, 55, 56, 59 also support achievement of BCR-ABL of 10% or less at 3 months as an important goal. Patients with this level of response at 3 months have an improved long-term outcome (EFS and OS) compared with those who have more than 10% transcripts. Although this has triggered recommendations for change in therapy for patients without this depth of response, no data suggest that the change in therapy alters the long-term outcome. Furthermore, even when those with slower responses have a worse outcome, the EFS at 5 years is approximately 80% in all series. Changing therapy for all represents an overreaction for most patients who will still have a favorable outcome. In fact, with additional assessment at 6 months, 30% to 50% will catch up in their response, and these patients have a similarly favorable outcome as if they had achieved the less than 10% BCR-ABL/ABL at 3 months.60 Adding more than one time point thus improves the prognostication abilities of early response. The rate of change of BCR-ABL transcripts in the first 3 months of therapy may also be important; patients with BCR-ABL greater than 10% at 3 months had superior outcomes if they had a halving time of less than 76 days.61 Patients who receive less than 80% of the target dose of imatinib, either because of dose reductions or because of missed doses, have a significantly lower probability of achieving the optimal response. Thus, at the moment, it is most prudent to minimize unnecessary treatment interruptions and dose reductions and to monitor patients carefully at early time points. No change in therapy is indicated until there is clear evidence of failure as defined by the ELN.

Definitions of Treatment Failure
Primary treatment failure can be defined as failure to achieve CHR and less than 95% Ph positive at 3 months, less than 10% BCR-ABL and Ph less than 35% at 6 months, or less than 1% BCR-ABL and CCyR at 12 months. This occurs in approximately 25% of imatinib-treated patients.19 Progression to AP and BP defines treatment failure at any point. Secondary treatment failure is loss of response after initially meeting treatment targets. Loss of response is defined as loss of CCyR, loss of CHR, or progression to AP and BP. Loss of response should not be defined on the basis of a single qRT-PCR result due to potential fluctuations inherent in testing method. Increasing molecular markers on 2 occasions should prompt further investigation.62, 63However, only 11% of patients in CCyR who have increasing molecular markers develop clinical events (loss of CCyR, loss of CHR, development of AP and BC), and switching TKIs has not been found to benefit patients with only molecular relapse but without loss of CCyR.64 Similarly, although ELN recommends the appearance of mutations to be considered treatment failure, it is not advised to investigate the presence of mutations unless there is clinical evidence of treatment failure. Furthermore, if a mutation were to be identified in a patient with adequate response, there is no evidence suggesting that change of therapy at that time improves outcome compared with change when clinical failure becomes evident, further supporting the recommendation to only test for mutations in instances of clinical failure.
Causes of treatment failure are diverse.65 Poor adherence is the most frequent cause of treatment failure and must be carefully evaluated. BCR-ABL mutations, which alter drug binding by directly altering an amino acid at the drug-binding site (eg, T315I, F317L, F359C/V) or indirectly by altering protein conformation (eg, G250E, Q252H, E255K/V), are crucial to identify because they determine sensitivity to salvage therapy and the subsequent choice of TKI. Other potential causes include pharmacokinetic interactions, such as accelerated TKI metabolism due to use of CYP3A4 hepatic enzyme inducers, or the use of proton pump inhibitors, which inhibit drug absorption. Diverse mechanisms may result in lower drug concentration within the cell despite adequate plasma levels, such as p-glycoprotein or ABCG2 drug efflux protein overexpression (affecting imatinib, nilotinib, and dasatinb), or low OCT1 activity, which is required for imatinib transportation into the cell (see earlier). Finally, overexpression of the Src kinase Lyn66 has been reported in some instances of resistance, but the incidence of this phenomenon is unknown.
Changes in BCR-ABL transcript levels may be associated with disease progression or development of resistance. However, identification of a sustained increase and an increasing trend are more important than a single increase, given the fluctuation that can occur in the assay results. In addition, the kinetics of change in BCR-ABL may vary according to the type of loss of response: patients with a rapid increase in BCR-ABL generally have disease progression to AP and BP or are nonadherent with therapy; in contrast, patients who have developed BCR-ABL1 mutations generally have a more gradual increase in BCR-ABL transcripts.63 An increase in BCR-ABL on a single occasion, particularly if the increase is greater than 5-fold or if MMR is lost, should prompt questioning regarding adherence to therapy and an early additional BCR-ABL qRT-PCR. If the rise is confirmed and adherence is not thought responsible, bone marrow aspiration should be performed to assess for the presence of disease progression, cytogenetic evolution, and BCR-ABL1 mutations. As mentioned previously, routine testing for mutations in patients with adequate response is not warranted. Even in the instance of suboptimal response or warning, mutations are identified in less than 5% of instances.

Treatment of Patients With Primary or Secondary Treatment Failure Who Remain in CP
Treatment of patients with refractory disease still in CP depends on several factors, particularly the type of initial therapy, the presence of BCR-ABL1 mutations, adherence, comorbidities, and eligibility for alloSCT.67 Patients who meet the definition of failure per the ELN have a shortened survival, with a median of approximately 5 years, and thus need a change in therapy.68 No randomized comparisons of switching to a second TKI compared with performing alloSCT exist, but our practice is to treat with at least a second TKI; patients are closely monitored. Although eligible patients for alloSCT should be considered for this approach if meeting failure criteria after a second TKI, in practice, most patients prefer to try a third TKI; still, a discussion about alloSCT should be held after initial failure.

Switching to a Second TKI
Six-year results of switching to dasatinib after imatinib failure or intolerance have been reported and reveal PFS and OS of 49% and 71% at 6 years, respectively. The CCyR rates were less than 50%, and the MMR rate was approximately 40% in long-term follow-up69; importantly, early responses (BCR-ABL <10% at 3 months) predicted longer-term outcomes. Comparable results have been reported with nilotinib, 400 mg twice daily, with the option to escalate to 600 mg twice daily, with a 4-year OS of 78%, PFS of 57%, and CCyR rate of 45%.70 Finally, bosutinib is active in imatinib-resistant patients, including all those with ABL1 mutations except T315I, at a dose of 500 mg/d; CCyR was achieved in 41% of patients with a 2-year PFS of 73% in imatinib-refractory patients and 95% in imatinib-intolerant patients. Bosutinib has an adverse effect profile that does not overlap substantially with the other TKIs, with the most frequent adverse events being diarrhea, rash, and biochemical liver function abnormalities.48 The drug is approved by the Food and Drug Administration for patients in whom at least one TKI has previously failed. Higher response rates to second-line TKI after imatinib failure are seen in patients with a low baseline Sokal risk score, greater depth of initial cytogenetic response with imatinib (particularly if CCyR was achieved), lack of recurrent neutropenia during imatinib therapy, and a good performance status.71, 72
Identification of specific BCR-ABL1 mutations is critical to subsequent TKI choice. Patients with a T315I mutation are resistant to all TKIs except ponatinib. Patients with the F317L mutation are resistant to dasatinib but responsive to nilotinib. Y253H, E255K/V, and F359V/C mutations are resistant to nilotinib but sensitive to dasatinib. There are no randomized studies to guide choice of subsequent TKI; however, changing to dasatinib is superior to increasing imatinib dose.73 Although the three second-generation TKIs have never been compared head to head, it appears that they have somewhat equivalent efficacy and can be selected based on known mutations, risk factors for toxicity, and schedule preferences. Still, despite the overall good results, less than 50% of patients achieve a CCyR with either of these drugs. Thus, better second-line treatment options are needed. In addition, for patients treated with second-generation TKI as frontline therapy, the results with any of these agents as second-line therapy are not known but are expected to be inferior to what is achieved when used after imatinib failure. Ponatinib is a logical candidate to fill this void, but unfortunately there is limited experience in this setting. Still, in instances of resistance to a second-generation TKI used as initial therapy, we usually select ponatinib as second line provided the patient does not have excessive risk factors for arteriothrombotic events. It is clear then that, despite the many good treatment options available in CML, new drugs or new approaches would still be welcome for the relatively small percentage of patients facing this clinical scenario.
Patients in whom 2 TKIs failed have more limited options, and treatment should be individualized. In the absence of BCR-ABL1 mutations predicted to produce resistance, nilotinib or dasatinib could be used, although there is limited, mostly retrospective, data with these agents. Bosutinib was prospectively investigated and is active in patients with failure of 2 previous TKIs, with a CCyR rate of 22% to 40% and 2-year PFS of 73%.74, 75 The PACE (Ponatinib Ph ALL and CML Evaluation) study found that 45 mg/d of ponatinib is highly active, achieving a 63% CCyR rate in a heavily pretreated population (>90% of patients had previously received at least 2 TKIs, and nearly 60% had previously received at least 3 TKIs). A subgroup analysis of the PACE study found equivalent efficacy for patients with the T315I mutation, who are resistant to all other TKIs.76Ponatinib has therefore been approved for patients with the T315I mutation or for whom no other TKI is indicated, under a risk evaluation and mitigation strategy, due to the risk of arterial thrombotic events.77Omacetaxine is a non-TKI protein synthesis inhibitor, given by subcutaneous injection for 14 days in a 28-day cycle, that is approved by the Food and Drug Administration for patients in whom 2 or more TKIs have failed.78In a phase 2 study in patients in whom 2 TKIs had previously failed, the rates of CHR, minor cytogenic response, and CCyR were 67%, 22%, and 4%, respectively79; in addition, the drug is active in patients with T315I mutation. In a separate phase 2 study, the rates of CHR and CCyR were 77% and 16%, respectively. However, PFS was only 7.7 months.80 The drug is associated with substantial myelosuppression.79, 80Although these results are more modest than those seen with TKIs, we use omacetaxine in instances where TKIs have failed or may not be indicated because of unacceptably high risk of specific adverse events.
AlloSCT should be considered for patients with CP-CML in whom 2 TKIs have failed. There are no data to guide the choice between third-line TKI or alloSCT, and this decision must therefore be individualized. However, the relatively low rates of CCyR and 2-year PFS with bosutinib and the risk of cardiovascular toxicity of ponatinib suggest that alloSCT should be considered in eligible patients; conversely, there are limited data on transplant outcomes in these heavily pretreated patients. A recent German CML study group study found that, provided they remain in CP, patients who undergo transplant after imatinib failure have excellent results post-alloSCT, with an 89% achievement of CMR after transplant, a treatment-related mortality of 6%, and a 3-year survival of 94%.81 Whether these impressive results can be replicated in patients who have experienced resistance to 2 or more TKIs remains to be seen.

Stopping Treatment in Patients With Prolonged CMR
Overall, 41% to 47% of patients who have been in continuous CMR for at least 24 months may remain with stable undetectable transcripts after ceasing imatinib.82, 83, 84 If recurrence up to the level of MMR is tolerated, the success rate increases to approximately 60%. Predictors of increased relapse likelihood in this setting include a high baseline Sokal risk score and a duration of imatinib therapy of less than 5 years.82 Continuous CMR for more than 64 months and treatment with a second-generation TKI may be associated with lower incidence of relapse after TKI cessation.84 Relapses occur most frequently within approximately 6 months; notably, most patients remain imatinib sensitive and regain CMR when use of the drug is recommenced.85However, the follow-up is still relatively short. Therefore, one needs to consider that late relapses after interferon therapy or alloSCT occurring more than 10 years after cessation of therapy may occur, and these are often in the lymphoid BP. Thus, continued monitoring is required, perhaps indefinitely, through peripheral blood PCR. Most patients who stop taking imatinib and maintain undetectable transcripts by standard qRT-PCR still have evidence of low-level disease when more sensitive, patient-specific DNA-based PCR assays are used.83 In addition, some patients have low-level fluctuation of BCR-ABL levels detected by standard RNA-based qRT-PCR, without experiencing true molecular relapse.85 The reasons for the lack of relapses in these patients are unclear, but it has been suggested that these patients may have an increased number of natural killer cells that may contribute to keeping the disease at bay.86
Although reported to be safe in relatively small numbers of patients in the clinical trial setting, this approach should only be undertaken in a clinical study or where a protocol for prospective, very close monitoring of patients is implemented to allow detection of early relapses and intervene promptly.

Treatment of AP-CML
Criteria for the diagnosis of AP-CML have been outlined earlier. ABL1 mutations increase in frequency in advanced-stage disease; mutational evaluation should therefore be performed and TKI choice based on this.62, 67 The optimal therapeutic approach in AP-CML differs according to whether the patient is TKI naive or has progressed from CP while taking a TKI. Eighty to ninety percent of treatment-naive patients will achieve CCyR with TKI87, 88 and have a similar EFS and OS to patients presenting in CP, particularly when treated with second-generation TKI. Those patients with cytogenetic clonal evolution as the only criterion for AP also have superior outcomes to those with hematologic and clinical features of AP.89 In contrast, much lower response rates and inferior EFS, with continued relapses, have been seen in studies of second-generation TKIs in patients with imatinib failure and AP disease.90, 91
Treatment options include a TKI or alloSCT (either de novo or after initial TKI therapy). There are no randomized data to guide the choice or dose of TKI. However, there is a suggestion from nonrandomized studies that second-generation TKIs have superior response rates to imatinib,87 and ponatinib provides perhaps the best outcome.
There are also no randomized data to guide the decision to perform alloSCT for patients with AP-CML. In the pre-imatinib era, patients transplanted in AP had 30% to 40% DFS at 4 years compared with 70% to 80% for CP.92, 93 Nonrandomized data suggest superior outcomes in patients treated with imatinib followed by alloSCT compared with imatinib alone, but there is the standard selection bias in this study.94
In summary, patients with de novo AP-CML may have good outcomes, particularly if treated with a second-generation TKI. We treat these patients following the same guidelines we use for CP patients, and alloSCT is only considered on failure of 2 TKIs. However, patients with AP developing after imatinib failure have significantly poorer outcomes and may be best treated more aggressively with a second-generation TKI followed by alloSCT when eligible. Patients with excellent, rapid responses to the second TKI may be followed up closely and alloSCT considered only if showing recurrence. Another important question for which there are no data to guide decisions is the role of maintenance TKI after transplant. Our practice is to continue prescribing TKI after transplant after count recovery for patients who previously progressed to AP or BP.

Treatment of BP-CML
Criteria for BP progression were outlined above. Approximately 50% to 60% of patients have myeloid blast phase (MBP) and 20% to 30% lymphoid blast phase (LBP). The remaining 10% to 30% are mixed.5 The aim of treatment is to achieve reversion to CP, then perform alloSCT with or without posttransplant TKI maintenance.

Treatment of LBP
Induction chemotherapy is given as per de novo ALL, with the addition of a TKI. Chemotherapy with hyperfractionated cyclophosphamide, vincristine, doxorubicin (adriamycin), and dexamethasone (hyper-CVAD) with a TKI can achieve CHR in approximately 90% of patients.95 Most patients will have previously received a TKI. However, in patients presenting with de novo transformation, it is important (although sometimes difficult) to distinguish CML in LBP from Ph-positive ALL. Morphologic criteria to suggest preexisting CML, such as monolobated megakaryocytes and basophilia, may be useful, as is the BCR-ABL transcript type; p210 BCR-ABL is present in most CML-LBP, whereas most Ph-positive ALL has the p190 transcript. Mutations in BCR-ABL1 in patients in whom imatinib therapy has failed are more frequent in BP (73%) relative to C and/AP96; the use of ABL1 mutational analysis to guide treatment is therefore essential. T315I is very frequent and, in contrast to CP, may be identified even before exposure to a TKI. These patients require treatment with ponatinib, usually combined with chemotherapy (hyper-CVAD, in our hands). Additional chromosomal abnormalities are frequent (particularly monosomy 7),95 and outcomes are generally poor. AlloSCT after initial response appears to improve outcomes, but selection bias in such studies is inevitable.96

Treatment of MBP
CML-MBP has a poor response to standard acute myeloid leukemia induction regimens.97 Patients with de novo MBP may respond to TKI monotherapy, but responses are shallow and transient.98, 99 There are few studies of AML induction chemotherapy or low-dose cytarabine combined with TKI.100, 101 Our general approach is to give standard acute myeloid leukemia induction chemotherapy with the addition of a TKI and perform alloSCT in responding patients.102 Although outcome for patients with prior BP is better when there is only minimal residual disease or no detectable disease even by PCR, we recommend alloSCT as soon as a patient is back to CP or has CHR because continued chemotherapy is no guarantee of improved response and may cause complications that can disqualify the patient for a later transplant.

Which TKI Should Be Used in BP-CML?
There are no head-to-head data in this area, and much existing data concern use of single-agent TKIs, which are rarely used in practice. Imatinib, 600 mg, results in shallow and transient single-agent responses.98, 99Imatinib does not cross the blood brain barrier and so is inadequate when central nervous system involvement exists.103, 104 Dasatinib, 140 mg/d, achieves a significantly higher rate of CCyR (26% and 46% in MBP and LBP, respectively), but responses are again transient, with a median survival of less than 12 months for MBP and less than 6 months for LBP.105 Although dasatinib crosses the blood brain barrier, we do not rely on this for prophylaxis or management of central nervous system disease and give standard treatment with intrathecal chemotherapy, high-dose systemic chemotherapy, and occasionally radiotherapy to approach this issue. Nilotinib, 400 mg twice daily, is associated with no better results compared with dasatinib and is not approved for this indication.70 Bosutinib is also approved for BP and may induce hematologic response in 28% and minor cytogenic response in 37%.106 Ponatinib has resulted in favorable response in heavily pretreated patients and patients with T315I mutations. Approximately 50% patients had a hematologic response after failure of dasatinib or nilotinib in MBP or LBP,107 and 18% achieved CCyR. The 1-year survival was an impressive 55%. Whenever possible, we use ponatinib because this might be the most effective agent and covers all mutations. Dasatinib and bostunib are suitable alternatives.

Treatment of Refractory and Relapsed BP
Novel agents for ALL, such as the CD22-immunoconjugate inotuzumab ozogamicin and the CD3/19 bispecific antibody blinatumomab, are yet to be evaluated because major studies have excluded Ph-positive patients. However, these could potentially be effective, as could CAR T cells directed against CD19, although there would likely be potential for antigen-negative escape or development of frank myeloid reversion, and any response would require consolidation with alloSCT.

Although CML remains one of the great success stories in modern oncology treatment, a number of challenges remain. Pre-treatment identification of patients likely to have poor outcomes is crude at best, and predictive tools to guide the optimal choice of TKI at baseline are not widely available, making treatment decisions largely empiric. Patients with failure of more than 1 TKI have relatively poor outcomes, and no data exist for second-line therapy for patients treated initially with a second-generation TKI. The mechanisms underlying the risk of arteriothrombotic events seen with several of the TKIs need to be better understood so that prevention and management can be approached more rationally. Finally, most patients require indefinite suppressive therapy, with an associated cumulative risk of potential toxic effects, particularly cardiovascular disease, as well as chronic, low-grade toxic effects that affect quality of life. Strategies to produce eradication of MRD, with minimal toxic effects, are essential to address these issues and to reduce the long-term pharmacoeconomic burden of indefinite TKI therapy.

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Leukemia’s Molecular Biography Uncovered in New Genomic Study

GEN 10/15/2015

  • Click Image To Enlarge +
    A new study offers a glimpse of the wealth of information that can be gleaned by combing the genome of a large collection of leukemia tissue samples. [hidesy/iStock]

    Researchers from the Dana-Farber Cancer Institute and the Broad Institute of MIT and Harvard have harnessed the power of next-generation sequencing to analyze a large collection of leukemia tissue samples. Using whole exome sequencing (WES), the investigators screened genetic material from more than 500 samples of chronic lymphocytic leukemia (CLL) and normal tissue—identifying dozens of genetic drivers for the disease, including two genes that had previously not been linked to human cancer.

    The investigators began to trace how some mutations affect the course of the disease and its susceptibility to treatment. Moreover, they started tracking the evolutionary path of CLL, as its dynamic genome spawns new groups and subgroups of tumor cells within a single patient.

    “Sequencing the DNA of CLL has taught us a great deal about the genetic basis of the disease,” explained senior author Catherine Wu, M.D., physician at Dana-Farber and associate professor of medicine at Harvard Medical School. “Previous studies, however, were limited by the relatively small number of tumor tissue samples analyzed, and by the fact that those samples were taken at different stages of the treatment process, from patients treated with different drug agents.

    Dr. Wu continued, stating “in our new study, we wanted to determine if analyzing tissue samples from a large, similarly-treated group of patients provides the statistical power necessary to study the disease in all its genetic diversity—to draw connections between certain mutations and the aggressiveness of the disease, and to chart the emergence of new mutations and their role in helping the disease advance.  Our results demonstrate the range of insights to be gained by this approach.”

    The findings from this study were published recently in Nature through an article entitled “Mutations driving CLL and their evolution in progression and relapse.”

    The researchers collected tumor and normal tissue samples from 538 patients with CLL, 278 of whom had participated in a German clinical trial that helped determine the standard treatment for the disease. After WES analysis, they uncovered dozens of genetic abnormalities that may play a role in CLL, including 44 mutated genes and 11 genes that were over- or under-copied in CLL cells. Interestingly, two of the mutated genes—RPS15 and IKZF3—have not previously been associated with human cancer.

    “This study also provides a vision of what the next phase of large-scale genomic sequencing efforts may look like,” noted lead author Dan Landau M.D., Ph.D., research fellow at Dana-Farber and the Broad Institute. “The growing sample size allows us to start engaging deeply with the complex interplay between different mutations found in any individual tumor, as well as reconstructs the evolutionary trajectories in which these mutations are acquired to allow the malignancy to thrive and overcome therapy.”

    Another fascinating discovery was that certain gene mutations were particularly common in tumor tissue from patients who had already undergone treatment, suggesting that these mutations help the disease rebound after initial therapy. In addition, the investigators found that therapy tends to produce shorter remissions in patients whose tumors carry mutations in the genes TP53 or SF3B1.

    “We found that genomic evolution after therapy is the rule rather than the exception,” Dr. Wu remarked. “Certain mutations were present in a greater number of leukemia cells within a sample after relapse, showing that these mutations, presumably, allow the tumor to persevere.”

    Dr. Wu and her colleagues hope that the findings from their studies will continue the push initiated by precision medicine to help personalize cancer treatments and develop new therapeutics.

    “The breadth of our findings shows what we will be able to achieve as we systematically sequence and analyze large cohorts of tumor tissue samples with defined clinical status,” stated co-senior author Gad Getz, Ph.D., director of the Cancer Genome Computational Analysis group at the Broad Institute. “Our work has enabled us to discover novel cancer genes, begin to chart the evolutionary path of CLL, and demonstrate specific mutations affect patients’ response to therapy. These discoveries will form the basis for precision medicine of CLL and other tumor types.”

Aurelian Udristioiu commented on Update on Chronic Myeloid Leukemia

 Update on Chronic Myeloid Leukemia  Larry H Bernstein, MD, FCAP, Curator LPBI Diagnosis and Treatment of Chronic …

In previous work the diagnosis of LAM-3 I made based on blood smears, the examination of bone marrow (BM) aspirates, the evaluation of promyeloblasts (greater than 30% in BM), and the presence of a specific immune phenotype. Immunocytochemical detection was performed to confirm the diagnosis of LAM-3 using FAR Leukemia kits (Italy), and there were positive results for the peroxidase reaction for promyelocytes, myelocytes, granulocytes, and peripheral blood cells (POX+) and negative results for the peroxidase reaction for the blast cells. We performed the leukocyte alkaline phosphatase reaction using a SIGMA kit ( to determine the neutrophil alkaline phosphatase (NAP) levels in granulocytes (negative or low values in LAM-3) and to evaluate the alpha-naphthyl-esterase reaction in monocytes cells (positive results indicate CMoL).
Lactate dehydrogenase (LDH) is an enzyme that is localized to the cytosol of human cells and catalyzes the reversible reduction of pyruvate to lactate via using hydrogenated nicotinamide deaminase (NADH) as co-enzyme. The causes of high LDH and high Mg levels in the serum include neoplastic states that promote the high production of intracellular LDH and the increased use of Mg²+ during molecular synthesis: Pyruvate acid>> LDH/NADH >>Lactate acid + NAD).
LDH is released from tissues in patients with physiological or pathological conditions and is present in the serum as a tetramer that is composed of the two monomers LDH-A and LDH-B, which can be combined into 5 isoenzymes: LDH-1 (B4), LDH-2 (B3-A1), LDH-3 (B2-A2), LDH-4 (B1-A3) and LDH-5 (A4). The LDH-A gene is located on chromosome 11, whereas the LDH-B gene is located on chromosome 12. The monomers differ based on their sensitivity to allosteric modulators. They facilitate adaptive metabolism in various tissues. The LDH-4 isoform predominates in the myocardium, is inhibited by pyruvate and is guided by the anaerobic conversion to lactate. Total LDH, which is derived from hemolytic processes, is used as a marker for monitoring the response to chemotherapy in patients with advanced neoplasm with or without metastasis.
The number of chromosome copies in malignant tumors can be correlated with the total serum LDH values. LDH levels in patients with malignant disease are increased as the result of high levels of the isoenzyme LDH-3 in patients with hematological malignant diseases and of the high level of the isoenzymes LDH-4 and LDH-5, which are increased in patients with other malignant diseases of tissues such as the liver, muscle, lungs, and conjunctive tissues. High concentrations of serum LDH damage the cell membrane.
In aerobic glucose metabolism, the oxidation of citric acid requires ADP and Mg²+, which will increase the speed of the reaction: Iso-citric acid + NADP (NAD) — isocitrate dehydrogenase (IDH) = alpha-ketoglutaric acid.
In the Krebs cycle (the citric cycle), IDH1 and IDH2 are NADP+-dependent enzymes that normally catalyze the inter-conversion of D-isocitrate and alpha-ketoglutarate (α-KG). The IDH1 and IDH2 genes are mutated in > 75% of different malignant diseases. Two distinct alterations are caused by tumor-derived mutations in IDH1 or IDH2: the loss of normal catalytic activity in the production of α-ketoglutarate (α-KG) and the gain of catalytic activity to produce 2-hydroxyglutarate (2-HG).
This product is a competitive inhibitor of multiple α-KG-dependent dioxygenases, including demethylases, prolyl-4-hydroxylase and the TET enzymes family (Ten-Eleven Translocation-2), resulting in genome-wide alternations in histones and DNA methylation.
IDH1 and IDH2 mutations have been observed in myeloid malignancies, including de novo and secondary AML (15%–30%), and in pre-leukemic clone malignancies, including myelodysplastic syndrome and myeloproliferative neoplasm (85% of the chronic phase and 20% of transformed cases in acute leukemia).
Today, the oncologists try a new drug, anti-IDH mutant, to treat AML..

Dr. Aurelian Udristioiu, MD,
Emergency County Hospital TARGU-JIU &USB University,
Primary Physician of Laboratory Medicine,
General Chemical Pathology, EuSpLM,
City Targu Jiu, Romania
National Academy of Biochemical Chemistry (NACB) Member,
Washington D.C, USA.

Aurelian Udristioiu commented on your update
” The IDH1 and IDH2 genes are mutated in > 75% of different malignant diseases. Two distinct alterations are caused by tumor-derived mutations in IDH1 or IDH2: the loss of normal catalytic activity. IDH1 and IDH2 mutations have been observed in myeloid malignancies, including de novo and secondary AML (15%–30%), and in pre-leukemic clone malignancies, including myelodysplastic syndrome and myeloproliferative neoplasm (85% of the chronic phase and 20% of transformed cases in acute leukemia). Today, the oncologists try a new drug, anti-IDH mutant, to treat AML.”

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Treatment for Chronic Leukemias [2.4.4B]

Larry H. Bernstein, MD, FCAP, Author, Curator, Editor[2.4.4B]

2.4.4B1 Treatment for CML

Chronic Myelogenous Leukemia Treatment (PDQ®)

Treatment Option Overview

Key Points for This Section

There are different types of treatment for patients with chronic myelogenous leukemia.

Six types of standard treatment are used:

  1. Targeted therapy
  2. Chemotherapy
  3. Biologic therapy
  4. High-dose chemotherapy with stem cell transplant
  5. Donor lymphocyte infusion (DLI)
  6. Surgery

New types of treatment are being tested in clinical trials.

Patients may want to think about taking part in a clinical trial.

Patients can enter clinical trials before, during, or after starting their cancer treatment.

Follow-up tests may be needed.

There are different types of treatment for patients with chronic myelogenous leukemia.

Different types of treatment are available for patients with chronic myelogenous leukemia (CML). Some treatments are standard (the currently used treatment), and some are being tested in clinical trials. A treatment clinical trial is a research study meant to help improve current treatments or obtain information about new treatments for patients with cancer. When clinical trials show that a new treatment is better than the standard treatment, the new treatment may become the standard treatment. Patients may want to think about taking part in a clinical trial. Some clinical trials are open only to patients who have not started treatment.

Six types of standard treatment are used:

Targeted therapy

Targeted therapy is a type of treatment that uses drugs or other substances to identify and attack specific cancer cells without harming normal cells. Tyrosine kinase inhibitors are targeted therapy drugs used to treat chronic myelogenous leukemia.

Imatinib mesylate, nilotinib, dasatinib, and ponatinib are tyrosine kinase inhibitors that are used to treat CML.

See Drugs Approved for Chronic Myelogenous Leukemia for more information.


Chemotherapy is a cancer treatment that uses drugs to stop the growth of cancer cells, either by killing the cells or by stopping them from dividing. When chemotherapy is taken by mouth or injected into a vein or muscle, the drugs enter the bloodstream and can reach cancer cells throughout the body (systemic chemotherapy). When chemotherapy is placed directly into the cerebrospinal fluid, an organ, or a body cavity such as the abdomen, the drugs mainly affect cancer cells in those areas (regional chemotherapy). The way the chemotherapy is given depends on the type and stage of the cancer being treated.

See Drugs Approved for Chronic Myelogenous Leukemia for more information.

Biologic therapy

Biologic therapy is a treatment that uses the patient’s immune system to fight cancer. Substances made by the body or made in a laboratory are used to boost, direct, or restore the body’s natural defenses against cancer. This type of cancer treatment is also called biotherapy or immunotherapy.

See Drugs Approved for Chronic Myelogenous Leukemia for more information.

High-dose chemotherapy with stem cell transplant

High-dose chemotherapy with stem cell transplant is a method of giving high doses of chemotherapy and replacing blood-forming cells destroyed by the cancer treatment. Stem cells (immature blood cells) are removed from the blood or bone marrow of the patient or a donor and are frozen and stored. After the chemotherapy is completed, the stored stem cells are thawed and given back to the patient through an infusion. These reinfused stem cells grow into (and restore) the body’s blood cells.

See Drugs Approved for Chronic Myelogenous Leukemia for more information.

Donor lymphocyte infusion (DLI)

Donor lymphocyte infusion (DLI) is a cancer treatment that may be used after stem cell transplant.Lymphocytes (a type of white blood cell) from the stem cell transplant donor are removed from the donor’s blood and may be frozen for storage. The donor’s lymphocytes are thawed if they were frozen and then given to the patient through one or more infusions. The lymphocytes see the patient’s cancer cells as not belonging to the body and attack them.



What`s new in chronic myeloid leukemia research and treatment?

Combining the targeted drugs with other treatments

Imatinib and other drugs that target the BCR-ABL protein have proven to be very effective, but by themselves these drugs don’t help everyone. Studies are now in progress to see if combining these drugs with other treatments, such as chemotherapy, interferon, or cancer vaccines (see below) might be better than either one alone. One study showed that giving interferon with imatinib worked better than giving imatinib alone. The 2 drugs together had more side effects, though. It is also not clear if this combination is better than treatment with other tyrosine kinase inhibitors (TKIs), such as dasatinib and nilotinib. A study going on now is looking at combing interferon with nilotinib.

Other studies are looking at combining other drugs, such as cyclosporine or hydroxychloroquine, with a TKI.

New drugs for CML

Because researchers now know the main cause of CML (the BCR-ABL gene and its protein), they have been able to develop many new drugs that might work against it.

In some cases, CML cells develop a change in the BCR-ABL oncogene known as a T315I mutation, which makes them resistant to many of the current targeted therapies (imatinib, dasatinib, and nilotinib). Ponatinib is the only TKI that can work against T315I mutant cells. More drugs aimed at this mutation are now being tested.

Other drugs called farnesyl transferase inhibitors, such as lonafarnib and tipifarnib, seem to have some activity against CML and patients may respond when these drugs are combined with imatinib. These drugs are being studied further.

Other drugs being studied in CML include the histone deacetylase inhibitor panobinostat and the proteasome inhibitor bortezomib (Velcade).

Several vaccines are now being studied for use against CML.

2.4.4.B2 Chronic Lymphocytic Leukemia

Chronic Lymphocytic Leukemia Treatment (PDQ®)

General Information About Chronic Lymphocytic Leukemia

Key Points for This Section

  1. Chronic lymphocytic leukemia is a type of cancer in which the bone marrow makes too many lymphocytes (a type of white blood cell).
  2. Leukemia may affect red blood cells, white blood cells, and platelets.
  3. Older age can affect the risk of developing chronic lymphocytic leukemia.
  4. Signs and symptoms of chronic lymphocytic leukemia include swollen lymph nodes and tiredness.
  5. Tests that examine the blood, bone marrow, and lymph nodes are used to detect (find) and diagnose chronic lymphocytic leukemia.
  6. Certain factors affect treatment options and prognosis (chance of recovery).
  7. Chronic lymphocytic leukemia is a type of cancer in which the bone marrow makes too many lymphocytes (a type of white blood cell).

Chronic lymphocytic leukemia (also called CLL) is a blood and bone marrow disease that usually gets worse slowly. CLL is one of the most common types of leukemia in adults. It often occurs during or after middle age; it rarely occurs in children.

Anatomy of the bone; drawing shows spongy bone, red marrow, and yellow marrow. A cross section of the bone shows compact bone and blood vessels in the bone marrow. Also shown are red blood cells, white blood cells, platelets, and a blood stem cell.

Anatomy of the bone. The bone is made up of compact bone, spongy bone, and bone marrow. Compact bone makes up the outer layer of the bone. Spongy bone is found mostly at the ends of bones and contains red marrow. Bone marrow is found in the center of most bones and has many blood vessels. There are two types of bone marrow: red and yellow. Red marrow contains blood stem cells that can become red blood cells, white blood cells, or platelets. Yellow marrow is made mostly of fat.

Leukemia may affect red blood cells, white blood cells, and platelets.

Normally, the body makes blood stem cells (immature cells) that become mature blood cells over time. A blood stem cell may become a myeloid stem cell or a lymphoid stem cell.

A myeloid stem cell becomes one of three types of mature blood cells:

  1. Red blood cells that carry oxygen and other substances to all tissues of the body.
  2. White blood cells that fight infection and disease.
  3. Platelets that form blood clots to stop bleeding.

A lymphoid stem cell becomes a lymphoblast cell and then one of three types of lymphocytes (white blood cells):

  1. B lymphocytes that make antibodies to help fight infection.
  2. T lymphocytes that help B lymphocytes make antibodies to fight infection.
  3. Natural killer cells that attack cancer cells and viruses.
Blood cell development. CDR526538-750

Blood cell development. CDR526538-750

Blood cell development; drawing shows the steps a blood stem cell goes through to become a red blood cell, platelet, or white blood cell. A myeloid stem cell becomes a red blood cell, a platelet, or a myeloblast, which then becomes a granulocyte (the types of granulocytes are eosinophils, basophils, and neutrophils). A lymphoid stem cell becomes a lymphoblast and then becomes a B-lymphocyte, T-lymphocyte, or natural killer cell.

Blood cell development. A blood stem cell goes through several steps to become a red blood cell, platelet, or white blood cell.

In CLL, too many blood stem cells become abnormal lymphocytes and do not become healthy white blood cells. The abnormal lymphocytes may also be called leukemia cells. The lymphocytes are not able to fight infection very well. Also, as the number of lymphocytes increases in the blood and bone marrow, there is less room for healthy white blood cells, red blood cells, and platelets. This may cause infection, anemia, and easy bleeding.

This summary is about chronic lymphocytic leukemia. See the following PDQ summaries for more information about leukemia:

  • Adult Acute Lymphoblastic Leukemia Treatment.
  • Childhood Acute Lymphoblastic Leukemia Treatment.
  • Adult Acute Myeloid Leukemia Treatment.
  • Childhood Acute Myeloid Leukemia/Other Myeloid Malignancies Treatment.
  • Chronic Myelogenous Leukemia Treatment.
  • Hairy Cell Leukemia Treatment

Older age can affect the risk of developing chronic lymphocytic leukemia.

Anything that increases your risk of getting a disease is called a risk factor. Having a risk factor does not mean that you will get cancer; not having risk factors doesn’t mean that you will not get cancer. Talk with your doctor if you think you may be at risk. Risk factors for CLL include the following:

  • Being middle-aged or older, male, or white.
  • A family history of CLL or cancer of the lymph system.
  • Having relatives who are Russian Jews or Eastern European Jews.

Signs and symptoms of chronic lymphocytic leukemia include swollen lymph nodes and tiredness.

Usually CLL does not cause any signs or symptoms and is found during a routine blood test. Signs and symptoms may be caused by CLL or by other conditions. Check with your doctor if you have any of the following:

  • Painless swelling of the lymph nodes in the neck, underarm, stomach, or groin.
  • Feeling very tired.
  • Pain or fullness below the ribs.
  • Fever and infection.
  • Weight loss for no known reason.

Tests that examine the blood, bone marrow, and lymph nodes are used to detect (find) and diagnose chronic lymphocytic leukemia.

The following tests and procedures may be used:

Physical exam and history : An exam of the body to check general signs of health, including checking for signs of disease, such as lumps or anything else that seems unusual. A history of the patient’s health habits and past illnesses and treatments will also be taken.

Complete blood count (CBC) with differential : A procedure in which a sample of blood is drawn and checked for the following:

The number of red blood cells and platelets.

The number and type of white blood cells.

The amount of hemoglobin (the protein that carries oxygen) in the red blood cells.

The portion of the blood sample made up of red blood cells.

Results from the Phase 3 Resonate™ Trial

Significantly improved progression free survival (PFS) vs ofatumumab in patients with previously treated CLL

  • Patients taking IMBRUVICA® had a 78% statistically significant reduction in the risk of disease progression or death compared with patients who received ofatumumab1
  • In patients with previously treated del 17p CLL, median PFS was not yet reached with IMBRUVICA® vs 5.8 months with ofatumumab (HR 0.25; 95% CI: 0.14, 0.45)1

Significantly prolonged overall survival (OS) with IMBRUVICA® vs ofatumumab in patients with previously treated CLL

  • In patients with previously treated CLL, those taking IMBRUVICA® had a 57% statistically significant reduction in the risk of death compared with those who received ofatumumab (HR 0.43; 95% CI: 0.24, 0.79; P<0.05)1

Typical treatment of chronic lymphocytic leukemia

Treatment options for chronic lymphocytic leukemia (CLL) vary greatly, depending on the person’s age, the disease risk group, and the reason for treating (for example, which symptoms it is causing). Many people live a long time with CLL, but in general it is very difficult to cure, and early treatment hasn’t been shown to help people live longer. Because of this and because treatment can cause side effects, doctors often advise waiting until the disease is progressing or bothersome symptoms appear, before starting treatment.

If treatment is needed, factors that should be taken into account include the patient’s age, general health, and prognostic factors such as the presence of chromosome 17 or chromosome 11 deletions or high levels of ZAP-70 and CD38.

Initial treatment

Patients who might not be able to tolerate the side effects of strong chemotherapy (chemo), are often treated with chlorambucil alone or with a monoclonal antibody targeting CD20 like rituximab (Rituxan) or obinutuzumab (Gazyva). Other options include rituximab alone or a corticosteroid like prednisione.

In stronger and healthier patients, there are many options for treatment. Commonly used treatments include:

  • FCR: fludarabine (Fludara), cyclophosphamide (Cytoxan), and rituximab
  • Bendamustine (sometimes with rituximab)
  • FR: fludarabine and rituximab
  • CVP: cyclophosphamide, vincristine, and prednisone (sometimes with rituximab)
  • CHOP: cyclophosphamide, doxorubicin, vincristine (Oncovin), and prednisone
  • Chlorambucil combined with prednisone, rituximab, obinutuzumab, or ofatumumab
  • PCR: pentostatin (Nipent), cyclophosphamide, and rituximab
  • Alemtuzumab (Campath)
  • Fludarabine (alone)

Other drugs or combinations of drugs may also be also used.

If the only problem is an enlarged spleen or swollen lymph nodes in one region of the body, localized treatment with low-dose radiation therapy may be used. Splenectomy (surgery to remove the spleen) is another option if the enlarged spleen is causing symptoms.

Sometimes very high numbers of leukemia cells in the blood cause problems with normal circulation. This is calledleukostasis. Chemo may not lower the number of cells until a few days after the first dose, so before the chemo is given, some of the cells may be removed from the blood with a procedure called leukapheresis. This treatment lowers blood counts right away. The effect lasts only for a short time, but it may help until the chemo has a chance to work. Leukapheresis is also sometimes used before chemo if there are very high numbers of leukemia cells (even when they aren’t causing problems) to prevent tumor lysis syndrome (this was discussed in the chemotherapy section).

Some people who have very high-risk disease (based on prognostic factors) may be referred for possible stem cell transplant (SCT) early in treatment.

Second-line treatment of CLL

If the initial treatment is no longer working or the disease comes back, another type of treatment may help. If the initial response to the treatment lasted a long time (usually at least a few years), the same treatment can often be used again. If the initial response wasn’t long-lasting, using the same treatment again isn’t as likely to be helpful. The options will depend on what the first-line treatment was and how well it worked, as well as the person’s health.

Many of the drugs and combinations listed above may be options as second-line treatments. For many people who have already had fludarabine, alemtuzumab seems to be helpful as second-line treatment, but it carries an increased risk of infections. Other purine analog drugs, such as pentostatin or cladribine (2-CdA), may also be tried. Newer drugs such as ofatumumab, ibrutinib (Imbruvica), and idelalisib (Zydelig) may be other options.

If the leukemia responds, stem cell transplant may be an option for some patients.

Some people may have a good response to first-line treatment (such as fludarabine) but may still have some evidence of a small number of leukemia cells in the blood, bone marrow, or lymph nodes. This is known as minimal residual disease. CLL can’t be cured, so doctors aren’t sure if further treatment right away will be helpful. Some small studies have shown that alemtuzumab can sometimes help get rid of these remaining cells, but it’s not yet clear if this improves survival.

Treating complications of CLL

One of the most serious complications of CLL is a change (transformation) of the leukemia to a high-grade or aggressive type of non-Hodgkin lymphoma called diffuse large cell lymphoma. This happens in about 5% of CLL cases, and is known as Richter syndrome. Treatment is often the same as it would be for lymphoma (see our document called Non-Hodgkin Lymphoma for more information), and may include stem cell transplant, as these cases are often hard to treat.

Less often, CLL may transform to prolymphocytic leukemia. As with Richter syndrome, these cases can be hard to treat. Some studies have suggested that certain drugs such as cladribine (2-CdA) and alemtuzumab may be helpful.

In rare cases, patients with CLL may have their leukemia transform into acute lymphocytic leukemia (ALL). If this happens, treatment is likely to be similar to that used for patients with ALL (see our document called Leukemia: Acute Lymphocytic).

Acute myeloid leukemia (AML) is another rare complication in patients who have been treated for CLL. Drugs such as chlorambucil and cyclophosphamide can damage the DNA of blood-forming cells. These damaged cells may go on to become cancerous, leading to AML, which is very aggressive and often hard to treat (see our document calledLeukemia: Acute Myeloid).

CLL can cause problems with low blood counts and infections. Treatment of these problems were discussed in the section “Supportive care in chronic lymphocytic leukemia.”

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Reporter: Aviva Lev-Ari, PhD, RN

Based on the results of a new study, researchers are developing a clinical trial to test imatinib(Gleevec) in patients with anaplastic large cell lymphoma (ALCL), an aggressive type of non-Hodgkin lymphoma that primarily affects children and young adults.

The researchers found that a protein called PDGFRB is important to the development of a common form of ALCL. PDGFRB, a growth factor receptor protein, is a target of imatinib. Imatinib had anticancer effects in both a mouse model of ALCL and a patient with the disease, Dr. Lukas Kenner of the Medical University of Vienna in Austria and his colleagues reported October 14 in Nature Medicine.

VIEW VIDEO by  Mayo Clinic Dr. Tim Call describes Chronic Lymphocytic Leukemia (CLL), its diagnosis, and treatment options for patients with CLL.

VIEW VIDEO  by Leading CLL researcher Dr. Thomas Kipps discusses the latest in the course of the disease including: symptoms, causes, and risk factors. Dr. Kipps also highlights discoveries made in his lab that may lead to developing new therapies to treat this disease. Series: “Stein Institute for Research on Aging” [9/2010] [Health and Medicine] [Show ID: 19345]

Understanding the Molecular Basis of Imatinib Mesylate Therapy in Chronic Myelogenous Leukemia and the Related Mechanisms of Resistance1

Commentary re: A. N. Mohamed et al., The Effect of Imatinib Mesylate on Patients with Philadelphia Chromosome-positive Chronic Myeloid Leukemia with Secondary Chromosomal Aberrations. Clin. Cancer Res., 9: 1333–1337, 2003.

  1. Guido Marcucci2,
  2. Danilo Perrotti, and
  3. Michael A. Caligiuri

+Author Affiliations

  1. Division of Hematology and Oncology, Department of Internal Medicine [G. M., M. A. C.], Division of Human Cancer Genetics, Department of Molecular Virology, Immunology and Medical Genetics [G. M., D. P., M. A. C.], The James Cancer Hospital and The Comprehensive Cancer Center at The Ohio State University, Columbus, Ohio 43210


CML3 is a myeloproliferative disorder with an incidence of approximately 1–1.5 cases/100,000 population/year, a slight male predominance, and a peak between 50 and 60 years of age (1) . This condition arises from a transformed pluripotent hematopoietic precursor associated with t(9;22)(q34;q11.2) that gives rise to the Ph′ chromosome. At the molecular level, this cytogenetic aberration results in the fusion of the ABL gene at chromosome band 9q34 with the BCR gene at chromosome band 22q11.2. The resultantBCR/ABL fusion gene encodes a chimeric protein necessary and sufficient to confer the leukemic phenotype. In a minority of the cases, despite absence of the Ph′ chromosome, molecular methodologies (i.e., fluorescence in situ hybridization, Southern, or RT-PCR) can still detect BCR/ABL as the product of complex cytogenetic aberrations involving other chromosomes in addition to 9q34 and 22q11.2, or cryptic genomic rearrangements of the BCR and ABL genes. Taken all together, >95% of the CML cases are associated with BCR/ABL expression that, therefore, represents the hallmark of this condition.

CML is a bi- or triphasic disease (2) . Patients usually present in a chronic proliferative phase characterized by splenomegaly and accumulation of neutrophils in their various stages of maturation. Basophils and blasts are normally <20% and 10%, respectively, in CP CML. Evolution to the BP (or blast crisis) is defined by an increase (≥20%) in myeloid or lymphoid blasts in blood, BM, or extramedullary locations. In many cases, the transformation is characterized by a passage through an AP, in which the failure of a patient to respond to therapy is accompanied by an increase in percentage of blasts (10–19%); a ≥20% increase in basophils, uncontrolled thrombocytosis, or thrombocytopenia; and acquisition of new cytogenetic abnormalities such as trisomy 8, isochromosome 17q, or a second Ph chromosome and/or genetic inactivation of the p53 gene.

The ultimate goal of treatment for CML is prevention of blast crisis, because, once this occurs, the prognosis is dismal. Although a rapid reduction of the white cell count can be achieved with chemotherapy (i.e., busulfan or hydroxyurea) in CP CML, these drugs usually fail to prevent disease progression. IFN-α was the first agent proven capable of modifying the biological history of CML by prolonging survival in patients who achieved CHR and MCR (<35% of Ph′+cells; Ref. 3 ). A second breakthrough in the treatment of CML occurred when 60–80% of patients undergoing alloBMT in CP were reported to be disease free at 5 years (456) . However, both IFN-α and alloBMT have considerable treatment-induced toxicity that attenuated the initial enthusiasm for these results, and novel, less toxic therapeutic strategies are being explored. In 2001, Druker et al. (7)reported the first Phase I study with imatinib mesylate (STI571, Gleevec), a specific inhibitor of BCR/ABL oncogenic activity. In this study, the authors demonstrated that high rates of CHR and MCR were achieved with relatively few side effects in patients with CML refractory or intolerant to IFN-α, opening new avenues for molecularly targeted therapies in this disease. Subsequently, encouraging results were also obtained for CML patients in BP (8) .

Is BCR/ABLthe Driving Force for Leukemogenesis in CML?

The transforming activity of BCR/ABL has long been demonstrated using in vitro and in vivo models. In initial studies, transfection of the BCR/ABL gene fusion resulted in malignant transformation of normal fibroblasts, and induced independent survival and proliferation in growth factor-dependent cell lines. Expression of BCR/ABL was also shown to be necessary and sufficient to induce leukemogenesis in animal models (reviewed in Ref. 9 ). Expression of BCR/ABL in mice was achieved by either introduction (“knock-in”) of the fusion gene in the mouse genome or by infecting murine stem cells with BCR/ABL-containing retroviral vectors. In knock-in transgenic mice with conditionalBCR/ABL expression, a low penetrance phenotype of acute B- or T-cell leukemia was reported. In contrast, in mice sublethally radiated and transplanted with syngeneic retrovirally transfected BCR/ABL+ stem cells, a condition mimicking human myeloproliferative disorders with neutrophil increase, BM expansion, hepatosplenomegaly, extramedullary hematopoiesis, and pulmonary leukostasis was observed.

How Does BCR/ABL Transform Cells?

The fusion partner ABL is a member of the nonreceptor tyrosine kinase family (10) . This gene encodes a protein containing a tyrosine kinase activity domain (SH1) in addition to two other regulatory domains (SH2 and SH3) that mediate protein-protein interaction and modulate activation of signal transduction. A nuclear localization domain is also present, supporting a shuttling activity of the ABL protein between cytoplasm and nucleus. Genetic disruption of ABL in mice results in lymphopenia, runting, and perinatal mortality. The other fusion partner, BCR, is a protein with multiple functional domains involved in oligomerization, SH-2 binding, serine/threonine kinase activity, and activation of members of the Rho small GTP-ase family of proteins (10) . Structural analysis of this gene suggests a role as a mediator of signaling transduction. With targeted disruption of BCR, mice have increased susceptibility to septic shock, but normal hematopoiesis.

In CML, each of the two partner genes are disrupted at specific breakpoints and fuse to create the chimeric BCR/ABL gene (11) . The most common rearrangements give rise to fusion transcripts identified as b2a2 or b3a2, which, in turn, are translated into a 210 kDa protein. Alternative BCR breakpoints can be located in minor cluster (m-BCR) or micro (μ) cluster (μ-BCR) regions and result in fusion transcripts that encode smaller (190 kDa) or larger (230 kDa) products, respectively. Although usually associated with Ph′+ acute lymphoblastic PiQO leukemia, the protein can also be detected in ≥90% of the CML patients from alternative splicing of p210. p230 is instead usually associated with CML patients presenting with an unusual predominance of neutrophils, resembling chronic neutrophilic leukemia. In each of these BCR/ABL variants, the ABL tyrosine kinase domain autophosphorylates and becomes constitutionally activated. Such BCR/ABLderegulated tyrosine kinase activity is, in fact, responsible for transformation of the hematopoietic stem cell and maintenance of the leukemic phenotype by recruiting and activating transducing signal pathways (i.e., RAS, RAF, extracellular signal-regulated kinase, c-Jun NH2-terminal kinase, phosphatidylinositol 3′-kinase, cCbl, CRKL, Janus-activated kinase-signal transducers and activators of transcription, PKC and PLCγ) involved in: (a) enhanced gene transcription (i.e., c-myc, c-Jun, reviewed in Ref. 12 ); (b) altered mRNA processing, nuclear export, and translation (i.e., bcl-xL, CAAT/enhancer binding protein α, and p53; reviewed in Ref. 13 , 14 ); and (c) increased or decreased protein stability (i.e., Abi proteins; DNA-PKcs; FUS, and hnRNP A1; reviewed in Ref. 13). This, in turn, leads to enhanced proliferative potential and survival, altered motility and trafficking, and suppression of granulocytic differentiation (1 , 13 , 15 , 16) .

Mechanisms of Action of Imatinib Mesylate

BCR/ABL is an ideal target for molecular targeted therapy, because this fusion protein is present in all of the CML cells, is absent from nonmalignant cells, and is necessary and sufficient to induce leukemia. Imatinib mesylate is a 2-phenylaminopyrimidine tyrosine kinase inhibitor with specific activity for ABL, platelet derived growth factor receptor, c-kit, and Albeson-related gene (17) . The pharmacological basis of this interaction has been elucidated by crystallographic studies. Imatinib mesylate binds to the amino acids of the BCR/ABL tyrosine kinase ATP binding site and stabilizes the inactive, non-ATP-binding form of BCR/ABL, thereby preventing tyrosine autophosphorylation and, in turn, phosphorylation of its substrates. This process ultimately results in “switching-off” the downstream signaling pathways that promote leukemogenesis. Preclinical in vitro and in vivo data indicated an impressive selective activity of imatinib mesylate on cells expressing BCR/ABL, and supported a rapid transition of this compound from the bench to the clinic.

To date, imatinib mesylate has been evaluated in several Phase I and II clinical trials of patients with IFN-α-resistant chronic, accelerated, or BP CML (7 , 8 , 181920) . From the collective analysis of these studies, imatinib mesylate appears to effectively induce high CHR and cytogenetic response rates with relatively few side effects. In patients with CP CML who have failed IFN-α the CHR was 95%, MCR 60%, and complete cytogenetic remission 46%. Notably, in these patients achievement of MCR at the 3-month time point correlated with improved progression-free survival. In AP and in blast crisis, the CHRs were 34% and 8%, MCRs were 24% and 16%, and complete cytogenetic remissions were 17%, and 7%, respectively. Disease progression was 11% at 18 months for CP, 40% at 12 months for AP, and 80% at 18 months for BP. Finally, preliminary data from an interim analysis of a phase III study of untreated CML patients randomized between imatinib mesylate versus IFN-α and ARA-C indicate a significantly better CHR, complete cytogenetic remission, and progression-free survival for the imatinib mesylate group after a median follow-up of 14 months (21) . However, a longer follow-up will be necessary to assess whether this compound can also impact on the natural history of the disease and prevent or delay transformation to blast crisis.

Mechanisms of Resistance to Imatinib Mesylate

During disease progression, CML progenitor cells acquire a number of genetic alterations, most probably because of increased genomic instability, that may explain the aggressive phenotype, chemotherapeutic drug resistance, and poor prognosis of CML in BP. Despite the exciting results obtained with imatinib mesylate noted above, CML patients eventually show resistance at a rate of 80% in BP, 40–50% in AP, and 10% in CP post-IFNα failure, at 2 years (19) . Identification of the molecular basis of resistance is important, because it could provide insight into disease progression and into the design of novel therapeutic strategies to prevent and overcome treatment resistance.

CML patients with imatinib mesylate resistance can be stratified into those with primary refractory disease, most frequently in accelerated or BPs, and those who relapse after initial response, who are most frequently in CP. On the basis of the presence or absence of BCR/ABL tyrosine kinase activity in leukemia cells, it is also possible to discriminate between cases with BCR/ABL-dependent and -independent mechanisms of imatinib mesylate resistance. Notably, because the BCR/ABL enzymatic activity cannot be easily measured in blood or BM patient samples, levels of phosphorylation of the BCR/ABL substrate CRKL have been used as a surrogate end point for the tyrosine kinase activity(22) .

In patients with higher levels of CRKL phosphorylation despite treatment with imatinib mesylate, resistance has been found to result from at least three different BCR/ABL-dependent mechanisms: BCR/ABL gene amplification, BCR/ABL mutations, and high plasma levels of AGP (reviewed in Ref. 23 ).

The association of BCR/ABL gene amplification with resistance to imatinib mesylate is consistent with the reliance of CML blast crisis cells on BCR/ABL expression/activity for their proliferation and survival, and with the reported enhanced expression of BCR/ABL in these cells (24) . Indeed, high levels of BCR/ABL expression, which are detected frequently in CML-blast crisis but not CP cells, appear to be required for suppression of myeloid differentiation and increased resistance to chemotherapy-induced apoptosis ofBCR/ABL-expressing cells. Specifically, high levels of BCR/ABL kinase activity are required for hnRNP E2-dependent inhibition of CAAT/enhancer binding protein α, the major regulator of granulocytic differentiation (25) , and for the La-dependent enhancement of MDM2 expression, which, in turn, results in functional inactivation of p53(14) , also required for myeloid blastic transformation (26 , 27) Although the mechanisms underlying such an increase of BCR/ABL expression are unclear, a double Ph′ chromosome is likely to be responsible for the enhanced BCR-ABL levels in some cases.

Other mechanisms of imatinib mesylate resistance involve mutations in the BCR/ABLgene itself. Several different mutations have been detected in at least 13 amino acids of the ATP-binding site or other regions of the tyrosine kinase domain, and the list is growing (23 , 28 , 29) . These mutations usually prevent imatinib mesylate from binding to BCR/ABL, thereby resulting in lack of inhibition of the tyrosine kinase activity. Among these mutations, substitution of a threonine to isoleucine at position 315 of ABL that prevents imatinib mesylate from binding to the ATP-binding domain, is the first described and one of the most frequent (22) .

A third mechanism of resistance relies on plasma levels of AGP. It has been shown that AGP binds imatinib mesylate at physiological concentrations in vitro and in vivo, and blocks the ability of imatinib mesylate to inhibit BCR/ABL kinase activity in a dose-dependent manner (reviewed in Ref. 23 ). Finally, in patients with primary refractoriness to imatinib mesylate, resistance more often occurs in absence of significant CRKL phosphorylation, suggesting activation of BCR/ABL-independent leukemogenic pathways.

In this issue, Mohamed et al. (30) hypothesized that clonal evolution, defined as acquisition of additional cytogenetic abnormalities other than t(9;22)(q34;q11), is a marker for genomic instability, and thereby, in this setting, additional “hits” can occur to activate BCR/ABL-independent leukemogenic mechanisms. Given this premise, CML patients with a more complex karyotype were expected to be more resistant to imatinib mesylate. To test their hypothesis, these authors analyzed 58 BCR/ABL-positive patients with IFN-α-resistant CP (n = 13), AP (n = 24), or BP (n = 21) CML with additional cytogenetic abnormalities who were each treated with imatinib mesylate. Of the 58 patients, 15 (CP = 46%; AP = 25%; BP = 14%) achieved a cytogenetic response, and 12 had a complete cytogenetic remission. With a follow-up of 17–30 months, 7 (12%) remained in complete remission on imatinib mesylate, supporting the notion that a subset of CML patients with t(9;22)(q34;q11) and additional cytogenetic abnormalities can achieve a sustained response. Because the molecular mechanisms of resistance in these patients were not fully evaluated, the contribution of additional cytogenetic abnormalities as an independent predictor of resistance to imatinib mesylate could not be directly addressed. Similar results were also reported in the imatinib mesylate initial studies (18 , 20) , and more recently by Schoch et al. (31) . These authors reported on 31 patients with additional chromosomal abnormalities present before the start of imatinib mesylate therapy. Additional cytogenetic abnormalities were less frequent in chronic than other phases of the disease (35.5% versus 68.8%; P = 0.0008), and when corrected for the difference in disease stage, they did not influence response to imatinib mesylate. These results have been confirmed recently by a larger study reported by Cortes et al. (32) where 498 CML patients in CP or AP were treated with imatinib mesylate. Of the 498, 121 had additional cytogenetic abnormalities. In a multivariate analysis at the 3-month time point, lack of cytogenetic response, but not presence of additional cytogenetic abnormalities, was found to be a negative prognostic factor for survival

Although a longer follow-up is necessary to draw definitive conclusions, these findings suggest that additional cytogenetic aberrations do not appear to impact on disease response, and, therefore, karyotype analysis should not be used to stratify patients for therapeutic alternatives to imatinib mesylate. Furthermore, despite clonal evolution, the oncogenic potential of BCR/ABL appears to remain the driving force for leukemogenesis, and, therefore, may continue to serve as a therapeutic target. Finally, in patients with additional cytogenetic abnormalities who are resistant to imatinib mesylate, evaluation for levels of CRKL-phosphorylation should be done to sort out the nature of the resistance to this treatment and to understand the interplay between BCR/ABL-dependent and -independent mechanisms in disease progression.

Concluding Remarks

The results obtained with imatinib mesylate to date are truly impressive, but longer follow-up will be necessary to establish whether prevention or delay of blast crisis can be achieved and whether an improved overall survival for the majority of patients with CML can be obtained. It is clear that complete cytogenetic remission is achievable in most patients with CP CML, and that those who do not achieve this important end point between 3 and 6 months are likely to have a poor outcome. However, in patients with complete cytogenetic remission, other challenges remain. In these patients, for instance, molecular remission defined as the absence of BCR/ABL fusion transcript by RT-PCR is usually not achieved. The reasons for persistent low levels of residual disease after imatinib mesylate and the prognostic significance of these findings are unknown. It is possible that small numbers of mutated and resistant BCR/ABL-positive subclones remain essentially unaffected by this treatment, and if a proliferation advantage is subsequently acquired in these cells, they may drive disease recurrence. Therefore, in patients with complete cytogenetic remission, monitoring of the BCR/ABL fusion transcript levels by quantitative RT-PCR has been suggested to predict impending relapse, and if rising levels of BCR/ABL expression are detected, consideration could be given to alternative strategies including alloBMT.

However, emerging data support the notion that hematologic or cytogenenetic remission can be achieved in imatinib-relapsed CP CML patients with higher doses of this agent. Kantarjian et al. reported on 54 patients with CML in CP who were initially treated with 400 mg of imatinib mesylate and, subsequently, with a higher dose (i.e., 800 mg) when hematologic or cytogenetic resistance or relapse developed (33) . Among 20 patients treated for hematologic resistance or relapse, 13 (65%) achieved CHR without complete cytogenetic remission, and among 34 patients treated for cytogenetic resistance or relapse, 19 (56%) achieved a complete cytogenetic remission or MCR. However, the mechanisms of resistance to standard dose were not evaluated in these patients and, therefore, correlation of these mechanisms with clinical response to the higher doses was not possible. Nevertheless, these data are intriguing and pose the question of whether a higher dose of imatinib mesylate could be used at the time of the initial diagnosis or during molecular relapse to prevent overt leukemia recurrence or blast transformation. Future studies will no doubt address these important issues. Regardless, it is undeniable that imatinib mesylate has changed our approach to CML and paved the way for additional molecular targeted strategies in leukemia.


  • 1 Supported in part by P30-CA16058, and K08-CA90469 Grants from the National Cancer Institute, Bethesda, MD, The Elsa U. Pardee Cancer Research Foundation, and The Coleman Leukemia Research Foundation.

  • 2 To whom requests for reprints should be addressed, at The Ohio State University, 458A Starling-Loving Hall, 320 West 10th Avenue, Columbus, OH 43210. Phone: (614) 293-7597; Fax: (614) 293-7527; E-mail:

  • 3 The abbreviations used are: CML, chronic myelogenous leukemia; Ph′, Philadelphia; ABL, Abelson; RT-PCR, reverse transcription-PCR; BM, bone marrow; CHR, complete hematologic remission; MCR, major cytogenetic response; alloBMT, allogeneic bone marrow transplantation; AGP, α1 glycoprotein; CP, chronic phase; AP, accelerated phase; BP, blastic phase.

  • Received March 3, 2003.
  • Accepted March 3, 2003.

Imatinib May Help Treat Aggressive Lymphoma

Based on the results of a new study, researchers are developing a clinical trial to test imatinib (Gleevec) in patients with anaplastic large cell lymphoma (ALCL), an aggressive type of non-Hodgkin lymphoma that primarily affects children and young adults.

The researchers found that a protein called PDGFRB is important to the development of a common form of ALCL. PDGFRB, a growth factor receptor protein, is a target of imatinib. Imatinib had anticancer effects in both a mouse model of ALCL and a patient with the disease, Dr. Lukas Kenner of the Medical University of Vienna in Austria and his colleagues reported October 14 in Nature Medicine.

The authors decided to investigate the effect of imatinib after finding a link between PDGFRB and a genetic abnormality that is found in many patients with ALCL. Previous work had shown that this genetic change—a translocation that leads to the production of an abnormal fusion protein called NPM-ALK—stimulates the production of two proteins, transcription factors called JUN and JUNB.

In the new study, experiments in mice revealed that these proteins promote lymphoma development by increasing the levels of PDGFRB.

Because imatinib inhibits PDGFRB, the authors tested the effect of the drug in mice with the NPM-ALK change and found that it improved their survival. They also found that imatinib given together with the ALK inhibitor crizotinib (Xalkori) greatly reduced the growth of NPM-ALK-positive lymphoma cells in mice.

To test the treatment strategy in people, they identified a terminally ill patient with NPM-ALK-positive ALCL who had no other treatment options and agreed to try imatinib. The patient began to improve within 10 days of starting the therapy and has been free of the disease for 22 months, the authors reported.

The observation that inhibiting both ALK and PDGFRB “reduces lymphoma growth and alleviates relapse rates” led the authors to suggest that the findings might be relevant to lymphomas with PDGFRB but without the NPM-ALK protein. “Our findings suggest that imatinib is a potential therapeutic option for patients with crizotinib-resistant lymphomas.”

A planned clinical trial will be based on the expression of PDGFRB in tumors.



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