Imaging Prostate Cancer
Posted: Nov 01, 2018
POSTED: April 03, 2018
“We can divide genomics into two different categories. The first category is germline genomics, which is the DNA with which you’re born. It’s clear that about 12% of people with advanced prostate cancer will have alterations in their inherited DNA, in particular in genes involved with DNA repair. Most common of these alterations are BRCA2. There are a variety of others that are somewhat prevalent, including ATM, CHEK2, and BRCA1. There are others that are more rare.
The implications of these germline mutations are significant for the patient: in certain configurations they may predispose a cancer to be sensitive to certain therapies, such as PARP inhibitors or platinum-based chemotherapy or (rarely) immunotherapy. There is more complexity, but knowing the germline mutation helps the informed clinician make decisions. In my practice, we test all patients with advanced prostate cancer for these germline mutations. (A National Comprehensive Cancer Network guideline suggests the same approach.)
These germline mutations represent the DNA with which you’re born. That DNA is going to have repercussions if also mutated in your family members. Men who have some of these DNA repair mutations have an increased risk of prostate cancer. In addition, there is a small increased risk of pancreatic cancer and male breast cancer for those with some of the germline mutations. Around 30% of men with BRCA2 will be diagnosed with prostate cancer in their lifetime, but that cancer is more likely to be aggressive if diagnosed. With regards to females, it’s particularly important. Females with DNA repair defects are more likely to have breast and ovarian cancer. Female with DNA repair mutations, in particular BRCA1/
BRCA2, ought to consider having their breasts or ovaries removed at an appropriate time. Prophylactic surgery has been demonstrated to be potentially life-saving for those individuals. The risk of breast cancer may be as high as 70% and the risk of ovarian cancer may be as high as 40%.
Thus, for these germline mutations there are implications for treatment and implications for the patient’s family.
We should be doing prostate cancer screening earlier in men with these DNA repair defects for prostate cancer; we should be doing biopsies at a PSA of 3 or higher, and perhaps even lower, for younger men known to be at risk. Starting screening at age 45 has been suggested by some. In addition to germline genomics, we need to also talk about somatic genomics. Data indicates that about 60% of individuals who have a DNA repair germline mutation are likely to have another second genetic mutation occur within their tumor. In addition, many of the tumors can acquire an alteration in their tumor DNA even when the germline is normal.
Taken together, about 20 to 25% of men may have DNA repair mutations in their tumor’s DNA. That makes them particularly sensitive to certain therapies such as the PARP inhibitors, as I mentioned earlier, or platinum chemotherapy. When you have two DNA repair mutations in the same cell, the likelihood of response to these agents appears fairly high.
There are also other DNA defects of considerable interest, such as alterations of the mismatch repair genes MSH-2 and MSH-6. When these alterations do occur, there is a potentially increased probability of responding to immunotherapy such as the new PD-1 inhibitors.
Overall, the guiding light today in genetics in my practice is to look at both the germline DNA and the tumor DNA. I choose to look at the tumor DNA circulating free DNA (cfDNA) tests, in particular the Guardant Health assay. The ability of other assays to corroborate the Guardant Health findings is not yet clear. There is clear data to indicate that different assays give different results, but nevertheless, I think in the early exploratory phase we’re in now, it’s important to begin to test patients in order to better understand their genomics and hopefully guide us towards better therapies. This will happen part of the time but certainly not all of the time.
There is more to the story of prostate cancer genetics. We’ve looked at androgen receptor mutations that can have implications for a response to Androgen Receptor directed therapy, such as Xtandi (enzalutamide), Zytiga (abiraterone), and Erleada (apalutamide). We’re dissecting a number of permutations that occur. It’s a complex scenario, because very few men have only one mutation. Most have multiple mutations. And in most cases, these mutations are not targetable with current therapies. This is very important for people to know.
Everybody thinks if they get a genomics test that means they’ve got a treatment. It’s not the case. Many times we get the genomics results and find that there are no known treatments we can use for that man’s particular alteration. That said, there is a subset of men who will have informative genomics while many more people will have non-informative genomics.
There is a final issue I’d like to discuss. There is currently a bit of a debate amongst physicians over the utility of PARP inhibitors such as Lynparza (olaparib) as compared to platinum chemotherapy. But it is noteworthy that platinum-based chemotherapies are inexpensive compared to PARP inhibitors. This does not require a clinical trial. (Most men will access PARP inhibitors through a clinical trial, although sometimes insurance companies are willing to try.)
As it turns out, neither the platinum-based chemotherapies nor the PARP inhibitors will be effective forever, so we do need strategies to manage patients after PARP inhibitors or platinum-based chemotherapies fail. Currently, that space is unexplored. We have to gather much more data before we can make conclusions about those with underlying DNA repair defects who have failed platinum-based chemotherapy or PARP inhibitors.
This is an area of active and important investigation that represents a conundrum for many patients today. I’ve got a patient right now going through this. We’re debating what to do next. I’ve tried to be as honest as I can when I say, “I don’t know what to do, but we’ve got to try something.”
We are in the middle of a revolution, but the parts and pieces are not yet clear. For some, understanding tumor genetics at the current level is helpful. For others, it is perplexing and expensive.
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