Dr. David J. VanderWeele is an Assistant Clinical Investigator in the Laboratory of Genitourinary Cancer Pathogenesis at the National Cancer Institute. He is particularly interested in investigating the progression of clinically significant prostate cancer.
Prostatepedia spoke with him about how genomics impacts patient care.
What is genomics, and how does it differ from genetics?
Dr. VanderWeele: Typically if you’re talking about genetics, you’re talking about an individual gene or a small set of genes. When you refer to genomics, you’re referring to all the genes or a very large set of genes. Genomics usually refers to the genes–the DNA sequence. But sometimes genomics is also used to refer to when those genes get expressed (as RNA), or to other changes to the DNA that don’t change the DNA sequence (also called epigenetics).
What do and don’t we know about why some men develop curable or indolent prostate cancers while some develop widely lethal diseases?
Dr. VanderWeele: A lot of effort has been put into trying to learn more about the genes you inherit from your parents and how that influences the likelihood that you’re diagnosed with cancer. Most of that effort has been unable to identify which alterations in your genes make it more likely that you will get an aggressive versus an indolent cancer.
As many of your readers probably know, many people get indolent prostate cancers. In fact, many autopsy studies have looked at patients who have died of other reasons and have never been diagnosed with prostate cancer. Once men reach their 70s or 80s, it looks like more than half of men develop prostate cancer. Of course, those are relatively slow-growing cancers.
The most information that we have now is that men who come from families with breast and ovarian cancer syndrome appear to be more likely to get cancer and more likely to get aggressive cancer. These involve BRCA1, BRCA2, and other DNA repair genes in a similar pathway. Though there aren’t FDA-approved therapies yet, there are trials suggesting that these patients are also more likely to respond to certain therapies approved for breast and ovarian cancer.
This is a pretty small subset of all the men with prostate cancer, but the percentages increase with any kind of measurement of aggressiveness. If you look at people with localized cancer, that percentage increases if you have high-grade cancer versus low-grade cancer. The percentage increases if you compare people with advanced castrate-resistant prostate cancer to those with localized cancer.
If you look at the length of time between a man’s diagnosis and when he dies, that rate increases significantly the shorter that time is. That is just looking at three of these genes, BRCA1, BRCA2, and ATM. If you look at a broader number of these DNA repair related genes, it looks like ten to twelve percent of all patients with castrate-resistant prostate cancer harbor a mutation that they inherited from their parents. It seems likely that for most of those patients, that inherited gene contributed to their prostate cancer.
That has led to some debate about how often we should test for mutations in these genes. Is that a high enough number that we should test everyone with castrate-resistant prostate cancer? Should we still rely on family history to provide guidance for which people should be tested?
Is it really expensive to test those men? Why wouldn’t you just go ahead and test?
Dr. VanderWeele: Depending on how you do it, testing costs have come down quite a bit.
But when you’re testing for genes that could potentially be passed on to your offspring, or that siblings or other family members may have inherited, there are implications for your other family members, not just for you.
Some members of your family may definitely want to know that information and think that more information is better. Others may feel that if they find out that they harbor that gene mutation, they will just feel like they’re waiting for the other shoe to drop. It’s not information that they’d want to know.
Generally, we advise people to get counseling to help them think through some of these issues before getting tested for genes they’ve inherited from their parents.
Do we know why some men respond to certain drugs and therapies and others don’t?
Dr. VanderWeele: There’s a lot of interest in that. There has been some progress made in terms of identifying the biomarkers that might suggest which patients are more likely to respond to which types of therapies. At this point, however, most patients still get treated with most therapies.
There are some genetic biomarker-driven therapies that look like they’re on the horizon. Patients with mutations in BRCA2, ATM, and related genes are more likely to respond to a type of therapy called PARP inhibitors, which are currently approved for patients with ovarian or breast cancer, but not yet for prostate cancer.
There was a single Phase II study that showed that patients who had loss of a specific tumor-suppressor gene called
PTEN are more likely to respond to a certain type of targeted therapy. There are larger ongoing trials to demonstrate that these are indeed predictive biomarkers for response to these therapies.
There are companies like FoundationOne and GenomeDX that look at the molecular features of a man’s cancer. Are those tests useful? What do they tell a patient?
Dr. VanderWeele: The FoundationOne test looks for mutations, deletions, or amplifications of specific genes that are relevant for a wide array of cancers. There are a lot of companies offering this type of sequencing.
Many hospitals offer their own version of it. A FoundationOne type of test can tell you if you have a mutation in BRCA2 or ATM. They should also be able to tell you if you have a deletion in PTEN. When they detect a mutation is present, however, generally they are not looking to determine if you inherited those changes from your parents versus the mutation being present only in the tumor cells.
These genetic tests are more popular in other types of cancers, because for prostate cancer there aren’t yet any FDA-approved therapies that would be given based on the results of these tests. These tests will become more popular as we make progress in demonstrating the benefit of these specific therapies and in our ability to predict which patients are most likely to respond.
If a patient reading this gets one of those tests, is it likely that his doctor is going to know what to do with the results? Will the results actually impact his treatment?
Dr. VanderWeele: There are probably a small number of patients who will have a result that will directly impact their therapy. At this point, the way that it would impact therapy is that it might suggest that they should find a clinical trial testing a specific type of drug.
I see.
Dr. VanderWeele: There are also other commercially available prostate specific genetic tests, like the one performed by GenomeDX, that are mostly aimed at men with localized prostate cancer who are trying to decide how aggressive their therapy should be. Typically, this means whether they should pursue active surveillance or get surgery or radiation.
Sometimes these tests are also used to determine if a patient should get radiation after undergoing a prostatectomy or if he should just continue to follow PSA numbers. The prostate specific gene expression tests are RNA-based tests, which are a little different.
They measure the levels of expression of a few specific genes. Tests like FoundationOne look for mutations, amplifications, or deletions of genes—which means they are DNA-based tests.
Tests like Decipher are more widely used now, right?
Dr. VanderWeele: Yes. They’re probably used mostly by urologists. My sense is that how often urologists order those tests and how heavily they rely on them versus other ways to predict the risk level of the prostate cancer varies quite a bit from urology practice to urology practice.
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