23 & You – Genetic tests for pca

The genetics of prostate cancer are daunting, but there are now a range of tests available that could be used at almost every stage of the disease IF you can deal with the answers you are likely to receive. Generally these tests are the product of science that goes something like this: A complete molecular picture is taken of all the mutations or all the genes expressed in a series of prostate cancer patients diagnosed years ago. For these patients “all you need to do” is go back to the paraffin blocks that were saved for each patient, extract the DNA/RNA and quantify gene expression and any mutations that can be detected. A decade ago, the technology for doing this was daunting, but now it is relatively easy. Once you have the gene expression profile, you can ask a computer to look for gene expressions that correlate with a certain outcome. For example, you take 500 patients from one center for whom the outcome is known…50 patients are dead, 32 from prostate cancer…70 patients developed metastases by 5 years…these 315 patients are alive and well with no evidence of recurrence…etc. Let’s say there are 50 genes that show changes in expression or mutation. Do we need all 50 to forecast what happened to the patients in that group? No. A computer algorithm can keep testing combinations and permutations of genes and reduce the 50 to a smaller number. We can either let the computer pick the final genes, or we could start with genes we think are related to tumor progression and then do the reduction. In the end, we have a small number of genes with characteristics that accurately separate the patients into “good” and “bad” groups and everything in between. We now take our gene panel, reduced to something like a computer chip and apply the test to 500 patients at another institution blinded from what actually happened to those patients. If our algorithm works, we should be able to accurately predict what happened to those patients in the next 5 or 10 years. If it works, our testing system has been validated, and we can begin offering the test to newly diagnosed patients at some stage of illness. For example, a Gleason 3+4=7 patient might fall into a group where surgery produced a 90% chance of being cured at 10 years, or a 40% chance depending on the gene expression. BUT…and this is key…what to do about the result is still a complex decision for both patient and physician. If you are a Gleason 3+3=6 patient and with no treatment at all you have an 85% chance of “cure” at ten years, is that good enough? What if it is a 95% chance? Will that make you more comfortable choosing no treatment, or do you want to be cured at any cost (impotence, incontinence, other side effects of radiation or surgery)?

As none of these tests has been proven in a prospective study – that is, using the tests to do something like even more aggressive therapy in a group of high risk patients, we are still in the early stages of understanding how and when to use them. Fortunately, my colleague, Dave Crawford and some colleagues have put together an excellent website to help patients/doctors understand the tests. http://www.pcmarkers.com has a list of most of the available tests and you can see what results might look like before you and your physician decide to send one off. This is a rapidly evolving field however, and not every test that is being commercialized is listed, and at big centers, there are always new tests being developed.

Finally, as with all of medicine, the payment systems/insurance coverage is crazily complex. Only today, I received an email with the “news” that a cardiologist/congressman, Rep. Buchson has introduced a bill called the “Prostate Cancer Misdiagnosis Elimination Act of 2017” that uses DNA profiling to make sure the tissue being tested is yours. You could theoretically apply this test to ANY cancer biopsy of course, so why prostate cancer? Then there is the motivation…call me cynical, but I suspected that the good congressman, meddling in medicine, might have a local connection, and sure enough, the company that markets the test is from his home state, Indiana. Not to say it isn’t important to know that tissue being tested comes from the correct patient or that the test isn’t a nice application of the kind of technology that identified OJ’s blood, just that we live in interesting times where medical technology is rapidly consuming more and more of our tax/insurance/personal dollars. Personalized medicine will depend totally on this type of technology and can be incredibly expensive. Whether it saves money or consumes it may depend on how many “worthless” (for that patient…and is a treatment with only a 5% chance of working really worthless??…not if you are in the 5% group) treatments are avoided and at what cost. I don’t have the answers. Hopefully this blog at least helps you begin to understand the current molecular diagnostic landscape.