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State of the art in oncologic imaging of Colorectal cancers.

Author-Writer: Dror Nir, PhD

This is the fourth post in a series in which I will address the state of the art in oncologic imaging based on a review paper; Advances in oncologic imaging that provides updates on the latest approaches to imaging of 5 common cancers: breast, lung, prostate, colorectal cancers, and lymphoma. This paper is published at CA Cancer J Clin 2012. © 2012 American Cancer Society.

The paper gives a fair description of the use of imaging in interventional oncology based on literature review of more than 200 peer-reviewed publications. In this post I summaries the chapter on colorectal cancer imaging. It reviews current and developing radiologic practices in CRC with respect to screening, preoperative evaluation, surveillance, and post-treatment re-staging.

Colorectal cancer (CRC) is an example to successful imaging-based screening evident by noticeable reduction in mortality rates. The 5-year survival rate of CRC patients diagnosed at an early stage is 90%.1 121 According to this review; “(CRC) is the third most common cancer worldwide and the second most frequent cause of cancer death in the United States. The American Cancer Society estimates that 143,460 new cases of CRC will be diagnosed and 51,690 deaths from CRC will occur in the United States in 2012.120 Because of screening and removal of premalignant polyps, incidence rates have declined over the last 3 decades.

The authors found out that the increased use of CT in CRC screening has the potential of reducing its costs and associated tisks 122 In addition, use of DW-MRI enabled better outcomes of CRC liver metastasis treatment as it enables tailored localized treatment of such lesions.123 124 Finally, the authors found that: “MRI for staging of rectal cancer has become standard practice and, in some instances, is performed in lieu of surgeon-performed endorectal US (ERUS), providing the radiologist with an even greater role in the management of patients with CRC.125 “

 Screening

CRC is a largely preventable disease, as the progression of the adenoma-carcinoma sequence of mutations is slow and leaves ample time to intervene. Nonetheless, approximately 41% of the population (in the USA) eligible for screening remains unscreened. 126 Most screening is performed using non-imaging tests”

Any of these screening strategies will reduce mortality from CRC.126127 

Among imaging tests used for screening, barium enema has seen a continual decline in usage, at least in part due to the landmark study showing that this test detected only 39% of polyps identified at colonoscopy, including only 48% of those > 1 cm in size.131 The recent (and largest, with > 2500 patients) multicenter CT colonography (CTC, also known as virtual colonoscopy) screening study, performed by the American College of Radiology Imaging Network, found that CTC had sensitivity of 90% and similar specificity for polyps > 9 mm, and the number of centers using CTC has increased.122 Widespread deployment of CTC remains hindered, in part, by the 2009 decision of the Center for Medicare and Medicaid Service (CMS) to deny reimbursement based on 1) potential radiation risk, 2) impact of detection of extracolonic findings, and 3) efficacy in the 65 years and older age group of concern to CMS. Data from studies reported after this decision put CTC in a good position to be reconsidered for reimbursement. The median estimated effective dose is currently 5 to 6 mSv, a dose far less than that received from a standard CT exam and even comparable to or lower than that received from a barium enema examination. In fact, the radiation dose from CTC is equivalent to that received from cosmic radiation in a 1-year period.132 Extra-colonic findings occur in 7% to 11% of cases and lead to extra examinations in about 6% with a relevant new diagnosis made in 2.5%, according to the experience of the largest screening center in the United States.133 Furthermore, when detection of extracolonic cancers and aortoiliac aneurysms is included along with CRC screening, CT colonography (CTC) has been shown to be more clinically effective and more cost-effective than optical colonoscopy.134 In an observational study, CTC accuracy was maintained in patients aged 65 to 79 years, who were compared to the overall general population sample. In the older patients, CTC remained a safe and effective modality and program outcome measures, such as colonoscopy referral and extracolonic work-up rates, remained similar to those in other screened groups.135

 Detection and Characterization

Diagnosis and clinical staging of primary colonic adenocarcinoma is most often accomplished by combining colonoscopy with biopsy and performing cross-sectional imaging to detect metastatic disease.

Although CT and MRI are widely used for preoperative whole-body staging, they are not recommended first-line methods for detection of primary lesions. In contradistinction, CTC has matured into an excellent diagnostic method for detection of CRC. Data drawn largely from screening studies tell us that its sensitivity for polyps > 10 mm is 90% or greater, and that it will detect nearly every cancer. In fact, a recent meta-analysis of more than 11,000 patients indicated that CTC had sensitivity of 96.1% (398 of 414) for CRC, and when cathartic cleansing and fecal tagging were used, no cancers were missed (Fig. 16).137 Detection of flat cancers remains a challenge with CTC as compared with endoscopic methods in which mucosal surface details are better appreciated. CTC not only detects CRC, but with its cross-sectional depiction also allows characterization of tumors using the TNM staging system138 with reasonable T- and N-stage accuracies of 83% and 80%, respectively.139 CTC is an operator-dependent technique that has shown great variability between radiologists with different degrees of training. Computer-aided detection (CAD) was developed for this reason and because 10,000 to 15,000 images must be scrutinized for each large adenoma detected. In a screening cohort of 3077 consecutive asymptomatic adults, stand-alone CAD had sensitivities of 97% and 100% for advanced neoplasia and cancer, respectively.140

Coronal reformatted CT scan of the abdomen and pelvis shows a left colon primary adenocarcinoma causing colonic obstruction.

Coronal reformatted CT scan of the abdomen and pelvis shows a left colon primary adenocarcinoma causing colonic obstruction.

Three-dimensional rendering from CT colonography shows a right colon adenocarcinoma which was stage T1N0.

Three-dimensional rendering from CT colonography shows a right colon adenocarcinoma which was stage T1N0.

With magnetic resonance colonography (MRC), detection of masses is limited because techniques employing air cause susceptibility artifacts, and those employing dark-lumen techniques with water-filling and intravenous gadolinium are under scrutiny because of concerns about the potential risk of nephrogenic systemic fibrosis. In addition, in the largest screening study, the sensitivity of MRC was only 70% in patients with colorectal lesions more than 10 mm in size.141

Imaging plays a critical role in detecting liver metastases in order to properly stage and treat the patient with colorectal cancer. NCCN guidelines recommend contrast-enhanced CT or MRI.142 “

MRI is the most promising imaging modality for management of rectal cancer.

Staging of this cancer is primarily accomplished with US, typically performed by surgeons. MRI using phased-array coils provides complete visualization of the pelvic anatomy and, especially, the circumferential resection margin, an important landmark for the standard total mesorectal excision.

In an MRI of rectal carcinoma, the T2-weighted axial image shows rectal mass penetrating the wall and extending to the left posterolateral mesorectal fascia (also known as the circumferential resection margin).

In an MRI of rectal carcinoma, the T2-weighted axial image shows rectal mass penetrating the wall and extending to the left posterolateral mesorectal fascia (also known as the circumferential resection margin).

 

 The MERCURY study125established the near equivalence of MRI to histopathology for identification of this margin, an important advantage of MRI over ERUS, with which the margin is not routinely visualized.147 T- and N- stage accuracies of MRI (87% and 74%, respectively) were similar to those of ERUS (82% and 74%, respectively).148 Accurate lymph node identification remains a problem for MRI. Toward this end, a new albumin-bound gadolinium agent has shown some promise, and further results are awaited.149

 Role of Imaging in Assessing Treatment Response

Imaging plays a critical role in 1) determining response to systemic and loco-regional treatment of liver metastases, 2) assessing response to local treatment and restaging rectal cancer primary lesions, and 3) detecting and assessing the treatment response of extra-hepatic metastatic disease. Systemic treatment (and in some centers, hepatic artery infusion) of non-resectable liver metastases with chemotherapy aims at reduction of the metastatic burden, which, occasionally may allow attempts at curative liver resection.

Due to the limitations of CT with regard to soft tissue contrast and fatty liver. MRI has greater sensitivity for remaining (or new) lesions < 1.0 cm due to its superior soft tissue contrast. In a recent meta-analysis of 25 eligible studies, MRI showed higher sensitivity than CT on a per-patient basis (P = .05) and on a per-lesion basis as well (P = .0001). With its 81.1% sensitivity and 97.2% specificity, MRI is thus the preferred modality.151 Nonetheless, under the current NCCN guidelines, CT remains the preferred modality.142 

Loco-regional (“liver-directed”) therapies include radiofrequency, microwave ablation, transarterial chemo- or particle embolization and irreversible electroporation. With these treatments, responding lesions can actually increase in size, and simple size criteria are no longer sufficient to determine response. The European Association for the Study of the Liver has issued new criteria to assess viability of remaining tumor based on enhancing residual volume by multiphase CT or MRI.152 However, the field is rapidly changing and there is no consensus on the optimal imaging strategy following loco-regional therapy.

Recent meta-analyses of randomized controlled trials comparing low-intensity and high-intensity surveillance programs have shown advantages for more intense follow-up in Stages I-III disease;170-173 however, controversies remain regarding the optimal surveillance strategy.

Lymphoma Imaging

To be followed…

Other research papers related to the management of Colorectal cancer were published on this Scientific Web site:

PIK3CA mutation in Colorectal Cancer may serve as a Predictive Molecular Biomarker for adjuvant Aspirin therapy

Personalized Medicine: Cancer Cell Biology and Minimally Invasive Surgery (MIS)

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