Today’s fundamental challenge in Prostate cancer screening
Author and Curator: Dror Nir, PhD
The management of men with prostate cancer is becoming one of the most challenging public health issues in the Western world. It is characterized by: over-diagnosis; over-treatment; low treatment efficacy; treatment related toxicity; escalating cost; and unsustainability [Bangma et al, 2007; Esserman et al, 2009]. How come? Well, everyone accepts that most prostate cancers are clinically insignificant. It is well known that all men above 65 harbor some sort of prostate cancer. Due to the current aggressive PSA-based screening, one in six men will be diagnosed with prostate cancer. Yet, the lifetime risk of dying of prostate cancer is only 3%. The problem is that, once diagnosed with prostate cancer, there is no accurate tool to identify those men that will die of the disease (in my previous post I mentioned 1:37). Currently, screening practices for prostate cancer are relying on the very unspecific prostate-specific-antigen (PSA) bio-marker test to determine which men are at higher risk of harboring prostate cancer and therefore need a biopsy. The existing diagnostic test is a transrectal ultrasound (TRUS) guided prostate biopsy aimed at extracting representative tissue from areas where cancer usually resides. This procedure suffers from several obvious faults:
1. Since the imaging tool used (B-mode ultrasound) is poor at detecting malignancies in the prostate, the probability of hitting a clinically significant cancer or missing a clinically insignificant cancer is subject to random error.
2. TRUS biopsy is also subjected to systematic error as it misses large parts of the prostate which might harbor cancer (e.g. apex and anterior zones).
3. TRUS guided biopsies are often unrepresentative of the true burden of cancer as either the volume or grade of cancer can be underestimated.
In the last ten years I was leading the development of an innovative ultrasound-based technology, HistoScanningTM, aimed at improving the aforementioned faults;
Among the other most popular imaging modalities aimed at better prostate cancer detection in routine use are: MRI, Elastography, Contrast Enhanced Ultrasound etc…
In my future posts I will go into more detail on how these imaging modalities fit into routine workflow, how much they stay within budget constraints and what level of promise they bear for promoting personalized medicine. Stay tuned… Footnote: According to the final report by an advisory panel to the USA government: Doctors should no longer offer the PSA prostate cancer screening test to healthy men because they’re more likely to be harmed by the blood draw, and the chain of medical interventions that often follows than be helped; (http://www.usatoday.com/news/health/story/2012-05-21/prostate-cancer-screening-test-harmful/55118036/1) But then; what should be offered instead?
Other posts on this Scientific Website addressing Prostate Cancer
Prostate Cancers Plunged After USPSTF Guidance, Will It Happen Again?
New Prostate Cancer Screening Guidelines Face a Tough Sell, Study Suggests
ROLE OF VIRAL INFECTION IN PROSTATE CANCER
http://pharmaceuticalintelligence.com/2012/09/01/role-of-viral-infection-in-prostate-cancer/
[…] See the original article here: Today's fundamental challenge in Prostate cancer screening … […]
Great images and like the Medical treatment related last sentences and the follow up post to wait for
This is an excellent presentation of improvement in imaging technology. I know that the debate about PSA and overdiagnosis has gone on for a good 15-20 years. Stamey presented his review of all the cases from his work at Stanford several years ago, and he was a developer of the sensitive method used today. He was disappointed with the results. He actually found that at a PSA level over 20+, the likelihood was that there is PC and that it is already metastatic. This was consistent with a study by MM Pinto et al. The difficulty then was that there was never validation of the best decision value for a PSA at the lower range, where medical decisions are made.
This is no longer the case. I cannot say more about a manuscript that should now be published in Clinical Biochemistry (Elsevier). (CLB-D-12-00159)
(Exciting and novel work).
Robustness of ProsVue™ linear slope for prediction of prostate cancer recurrence: Simulation studies on effects of analytical imprecision and sampling time variation
The authors present support for a method of use of the ProsVue linear slope for predicting PCa recurrence or survival within 8 years Post-RP. The 8 year time frame is validated using a small study, and treating the sample size problem using simulation of the predictors consisting of the mean and SDs of 3 PSA values taken postoperatively, and the log transform when Gaussian distribution is not found. The dependent variable in establishing the measured slope variances is whether or not there is recurrence.
Dr. Nir,
I added references for three posts on Prostate Cancer on this Site
Thanks Aviva,
I’ve read them. Great support to the claim that PSA screening is not suitable. If you combine inadequate screening with inadequate diagnosis (which was the subject of my post) you get the overtreatment situation Prostate cancer patients are in today.
Dror Nir, PhD
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Great to anticipate interesting post.
Very happy you joined my team. I posted to all my groups this post, will do it again on WED when all are at their desktop in the US
The main problem of PSA screening, as everybody knows, is that PSA was developed to detect recurrences! not early cancer still developing inside a functional prostate. Studies that I have conducted with HistoScanning showed that combining PSA with imaging based tissue characterization results with a much better correlation between cancer progression and PSA progression. I’ll probably get to it in one of my future posts…
PUT IT IN CONTEXT OF CANCER CELL MOVEMENT
The contraction of skeletal muscle is triggered by nerve impulses, which stimulate the release of Ca2+ from the sarcoplasmic reticuluma specialized network of internal membranes, similar to the endoplasmic reticulum, that stores high concentrations of Ca2+ ions. The release of Ca2+ from the sarcoplasmic reticulum increases the concentration of Ca2+ in the cytosol from approximately 10-7 to 10-5 M. The increased Ca2+ concentration signals muscle contraction via the action of two accessory proteins bound to the actin filaments: tropomyosin and troponin (Figure 11.25). Tropomyosin is a fibrous protein that binds lengthwise along the groove of actin filaments. In striated muscle, each tropomyosin molecule is bound to troponin, which is a complex of three polypeptides: troponin C (Ca2+-binding), troponin I (inhibitory), and troponin T (tropomyosin-binding). When the concentration of Ca2+ is low, the complex of the troponins with tropomyosin blocks the interaction of actin and myosin, so the muscle does not contract. At high concentrations, Ca2+ binding to troponin C shifts the position of the complex, relieving this inhibition and allowing contraction to proceed.
Figure 11.25
Association of tropomyosin and troponins with actin filaments. (A) Tropomyosin binds lengthwise along actin filaments and, in striated muscle, is associated with a complex of three troponins: troponin I (TnI), troponin C (TnC), and troponin T (TnT). In (more ) Contractile Assemblies of Actin and Myosin in Nonmuscle Cells
Contractile assemblies of actin and myosin, resembling small-scale versions of muscle fibers, are present also in nonmuscle cells. As in muscle, the actin filaments in these contractile assemblies are interdigitated with bipolar filaments of myosin II, consisting of 15 to 20 myosin II molecules, which produce contraction by sliding the actin filaments relative to one another (Figure 11.26). The actin filaments in contractile bundles in nonmuscle cells are also associated with tropomyosin, which facilitates their interaction with myosin II, probably by competing with filamin for binding sites on actin.
Figure 11.26
Contractile assemblies in nonmuscle cells. Bipolar filaments of myosin II produce contraction by sliding actin filaments in opposite directions. Two examples of contractile assemblies in nonmuscle cells, stress fibers and adhesion belts, were discussed earlier with respect to attachment of the actin cytoskeleton to regions of cell-substrate and cell-cell contacts (see Figures 11.13 and 11.14). The contraction of stress fibers produces tension across the cell, allowing the cell to pull on a substrate (e.g., the extracellular matrix) to which it is anchored. The contraction of adhesion belts alters the shape of epithelial cell sheets: a process that is particularly important during embryonic development, when sheets of epithelial cells fold into structures such as tubes.
The most dramatic example of actin-myosin contraction in nonmuscle cells, however, is provided by cytokinesisthe division of a cell into two following mitosis (Figure 11.27). Toward the end of mitosis in animal cells, a contractile ring consisting of actin filaments and myosin II assembles just underneath the plasma membrane. Its contraction pulls the plasma membrane progressively inward, constricting the center of the cell and pinching it in two. Interestingly, the thickness of the contractile ring remains constant as it contracts, implying that actin filaments disassemble as contraction proceeds. The ring then disperses completely following cell division.
Figure 11.27
Cytokinesis. Following completion of mitosis (nuclear division), a contractile ring consisting of actin filaments and myosin II divides the cell in two.
http://www.ncbi.nlm.nih.gov/books/NBK9961/
This is good. I don’t recall seeing it in the original comment. I am very aware of the actin myosin troponin connection in heart and in skeletal muscle, and I did know about the nonmuscle work. I won’t deal with it now, and I have been working with Aviral now online for 2 hours.
I have had a considerable background from way back in atomic orbital theory, physical chemistry, organic chemistry, and the equilibrium necessary for cations and anions. Despite the calcium role in contraction, I would not discount hypomagnesemia in having a disease role because of the intracellular-extracellular connection. The description you pasted reminds me also of a lecture given a few years ago by the Nobel Laureate that year on the mechanism of cell division.
PUT IT IN CONTEXT OF CANCER CELL MOVEMENT
The contraction of skeletal muscle is triggered by nerve impulses, which stimulate the release of Ca2+ from the sarcoplasmic reticuluma specialized network of internal membranes, similar to the endoplasmic reticulum, that stores high concentrations of Ca2+ ions. The release of Ca2+ from the sarcoplasmic reticulum increases the concentration of Ca2+ in the cytosol from approximately 10-7 to 10-5 M. The increased Ca2+ concentration signals muscle contraction via the action of two accessory proteins bound to the actin filaments: tropomyosin and troponin (Figure 11.25). Tropomyosin is a fibrous protein that binds lengthwise along the groove of actin filaments. In striated muscle, each tropomyosin molecule is bound to troponin, which is a complex of three polypeptides: troponin C (Ca2+-binding), troponin I (inhibitory), and troponin T (tropomyosin-binding). When the concentration of Ca2+ is low, the complex of the troponins with tropomyosin blocks the interaction of actin and myosin, so the muscle does not contract. At high concentrations, Ca2+ binding to troponin C shifts the position of the complex, relieving this inhibition and allowing contraction to proceed.
Figure 11.25
Association of tropomyosin and troponins with actin filaments. (A) Tropomyosin binds lengthwise along actin filaments and, in striated muscle, is associated with a complex of three troponins: troponin I (TnI), troponin C (TnC), and troponin T (TnT). In (more ) Contractile Assemblies of Actin and Myosin in Nonmuscle Cells
Contractile assemblies of actin and myosin, resembling small-scale versions of muscle fibers, are present also in nonmuscle cells. As in muscle, the actin filaments in these contractile assemblies are interdigitated with bipolar filaments of myosin II, consisting of 15 to 20 myosin II molecules, which produce contraction by sliding the actin filaments relative to one another (Figure 11.26). The actin filaments in contractile bundles in nonmuscle cells are also associated with tropomyosin, which facilitates their interaction with myosin II, probably by competing with filamin for binding sites on actin.
Figure 11.26
Contractile assemblies in nonmuscle cells. Bipolar filaments of myosin II produce contraction by sliding actin filaments in opposite directions. Two examples of contractile assemblies in nonmuscle cells, stress fibers and adhesion belts, were discussed earlier with respect to attachment of the actin cytoskeleton to regions of cell-substrate and cell-cell contacts (see Figures 11.13 and 11.14). The contraction of stress fibers produces tension across the cell, allowing the cell to pull on a substrate (e.g., the extracellular matrix) to which it is anchored. The contraction of adhesion belts alters the shape of epithelial cell sheets: a process that is particularly important during embryonic development, when sheets of epithelial cells fold into structures such as tubes.
The most dramatic example of actin-myosin contraction in nonmuscle cells, however, is provided by cytokinesisthe division of a cell into two following mitosis (Figure 11.27). Toward the end of mitosis in animal cells, a contractile ring consisting of actin filaments and myosin II assembles just underneath the plasma membrane. Its contraction pulls the plasma membrane progressively inward, constricting the center of the cell and pinching it in two. Interestingly, the thickness of the contractile ring remains constant as it contracts, implying that actin filaments disassemble as contraction proceeds. The ring then disperses completely following cell division.
Figure 11.27
Cytokinesis. Following completion of mitosis (nuclear division), a contractile ring consisting of actin filaments and myosin II divides the cell in two.
http://www.ncbi.nlm.nih.gov/books/NBK9961/
This is good. I don’t recall seeing it in the original comment. I am very aware of the actin myosin troponin connection in heart and in skeletal muscle, and I did know about the nonmuscle work. I won’t deal with it now, and I have been working with Aviral now online for 2 hours.
I have had a considerable background from way back in atomic orbital theory, physical chemistry, organic chemistry, and the equilibrium necessary for cations and anions. Despite the calcium role in contraction, I would not discount hypomagnesemia in having a disease role because of the intracellular-extracellular connection. The description you pasted reminds me also of a lecture given a few years ago by the Nobel Laureate that year on the mechanism of cell division.
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Many thanks,Annette
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Open Journals vs. Subscription-based « Pharmaceutical Intelligenceâ, very compelling plus the blog post ended up being a good read.
Many thanks,Annette
I actually consider this amazing blog , âSAME SCIENTIFIC IMPACT: Scientific Publishing –
Open Journals vs. Subscription-based « Pharmaceutical Intelligenceâ, very compelling plus the blog post ended up being a good read.
Many thanks,Annette