Michael J. Pishvaian, MD, PhD
Molecular biomarkers are gaining significance in the gastrointestinal (GI) cancer realm outside of HER2
overexpression, including BRCA, NTRK, PALB2,
and microsatellite instability (MSI). Now, researchers are exploring how they can best be targeted—and how to optimally detect them.
State of the Science Summit™ on Gastrointestinal Cancers, Michael J. Pishvaian, MD, an oncologist at Georgetown-Lombardi Comprehensive Cancer Center, discussed expanded testing for biomarkers, using liquid biopsies to predict response to treatment, and the importance of identifying increasingly specific subsets of GI cancers to make treatment decisions.
OncLive: What are the latest developments in precision medicine?
What we are looking for are predictive biomarkers that lead us toward specific therapies. The term “actionability” is often used to describe a biomarker that predicts full responsiveness, or at least a high responsiveness to a certain therapy. Sometimes that therapy is approved and used in the cancer that is being treated, and sometimes it’s approved and used in a different cancer. Ultimately, that biomarker seems to have promise in the cancer you are treating.
I do have a couple of things to [focus on] with regard to liquid biopsies. I'm a little biased because we looked at liquid biopsies, at least in pancreatic cancer, and we found what a lot of other people have found. Liquid biopsies have tremendous potential, but because they're not very sensitive tests, you need to know what you're looking for. If you know the mutation you're looking for, it’s a great test to use because it’s very specific. However, if you need to look broadly, it’s more difficult because the technology does not allow you to use this broad profiling into the tumor cell. At least in the world of GI cancers, I still prefer to look in the tumor if I can— and in the blood if I have no other choice.
How soon can we expect widespread adoption of expanded testing and liquid biopsies?
There's a great deal of adoption of liquid biopsies because they're so easy to do. The problem is that we need to couple that with a lot of education. If you don't find what you're looking for—a negative answer—a lack of identification doesn't necessarily mean it’s not there. I have to go to my lung cancer colleagues to give an example of this. In lung cancer today, there are 3 mutations that have to be tested for in treatment. If a liquid biopsy is done and shows a mutation, they don't have to do any further testing. If no mutation is found, it might be a result of lack of sensitivity and they’d have to look in the tumor. If we find a KRAS
mutation in colon cancer in the blood, we're done; however, if we don't see one, it still might be present.
When is the best time to perform a liquid biopsy?
If there's tumor available, there's no good time to do a liquid biopsy in GI cancers. If there's absolutely no opportunity to get to the patient's tumor because they have metastatic disease, then we'll certainly work around it. There is a separate discussion about liquid biopsies and some intriguing emerging data about tracking response to therapy. In KRAS
mutations, you can have very high levels of KRAS
-mutated DNA in the blood and that level can plummet when treated effectively. It may actually become an early marker of response to therapy even before you get that first test scan. That is definitely a very useful way to use liquid biopsies, but we need good data and studies to prove that.
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