Dr. Michael K. Brawer talks about Prolaris, a molecular diagnostic test for prostate cancer
How does Prolaris fit into the spectrum of prostate cancer molecular biomarkers?
Dr. Brawer: Prolaris is a molecular biomarker that quantitates cell cycle progression genes. That is to say it measures 31 genes related to the process that tells a cell to divide into two cells and then the two cells to go to four cells, etc. (This process is called mitosis.)
Dr. Steve Stone, a very smart molecular biologist, decided to look at these cell cycle progression genes for prostate cancer, because these are the genes that provide the majority of meaningful information in breast cancer prognostic signatures.
What is important about these genes? If you ask a fourth grader, “What is cancer?” he mostly likely is going to tell you cancer is what happens when cells grow out of control. That is what makes it cancer: the control of the division of the cells, or the mitosis, has gone amuck and now you’ve got unfettered proliferation.
More importantly, in the process of dividing and multiplying cells, mutations that arise in one cell get passed on to the daughter cell. That is how cancer progresses down its path from an incipient cancer to a cancer that may kill the patient. This passing on of genetic information that accrues through mutations makes cancer progress into a lethal type of cancer.
Prolaris is a test done on tissue obtained from a diagnostic biopsy or a radical prostatectomy. The clinician sends the specimen to Myriad Genetics where we quantitate the expression of these genes and adjust for other genes, which are constantly expressed. We can tell whether a man has more of these 31 genes or less than these 31 genes expressed at a stable rate.
We’ve now published data on nine cohorts in several publications; we’ve looked at men treated with everything from watchful waiting to radical prostatectomy to external beam radiation therapy. We have shown in all the studies that Prolaris is either the dominant predictor or the co-dominant predictor of whether the man does well with his prostate cancer, dies, develops metastasis, or fails either radiation or radical prostatectomy by having PSA progression.
How are Prolaris’ results used in the clinic?
Dr. Brawer: You raise an important point. If the test makes no difference, why do the test?
We’ve published three utility studies. These utility studies ask, “How was the man going to be treated before the clinician got the Prolaris result” versus, “How was the patient actually treated after the clinician received the results?”
Overall, well over half the patients in all three studies received a different treatment after the Prolaris result then they would have before the test.
So then it does change treatment decisions?
Dr. Brawer: Right.
For example, say a 55-year-old man has a Gleason 3+3 prostate cancer, his PSA is 12, and he has T1C disease.
A urologist sees him. The urologist says, “Based on what I see here, I recommend a prostatectomy.” The patient could then say, “My golfing partner had a test called Prolaris. I’d like to get that, as well.” He gets a Prolaris test; there is a whole host of information provided in the result.
With Prolaris, we show the chance that a man will die of prostate cancer. We can do that because we have data on three cohorts of men initially treated conservatively who were then followed for a median of about a decade. We can see who ended up dying of the disease.
Let’s say this patient who was originally going to get a radical prostatectomy finds out through Prolaris that his prostate cancer is considered low aggressive.
Then his doctor can confidently recommend active surveillance because the chance that he is going to progress is extremely low. This particular patient may do fine for the rest of his life just having periodic examinations. He doesn’t need aggressive treatment. The opposite scenario is also possible.
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