Expert Perspectives of a 67-Year-Old Man with Metastatic HER2+ Gastric Cancer - Episode 2

Molecular Testing for Metastatic HER2+ Gastric Cancer

John Marshall, MD

An expert in gastric cancers describes when and for whom molecular testing should be done in patients with metastatic HER2+ gastric cancer, and which tests are move relevant to treatment decision-making.

John Marshall, MD: This is a typical case and course for a patient with HER2-positive metastatic gastroesophageal cancer. We know that molecular testing is incredibly important for our patients with upper GI [gastrointestinal] cancers and is now required before anyone starts front-line therapy. You got to know HER2. You need to know PD-L1 [programmed death-ligand 1]. You need to know microsatellite stability or instability [MSI]. This is a very common type of patient that we all would see in front-line. Age is appropriate. The genetic testing symptoms are all appropriate. I think the good positive finding here is that when you do have a target such as HER2, the therapy is effective. It's more effective than traditional chemotherapy on its own. You don't want to miss the opportunity to identify these patients.

As I said, molecular testing for HER2, PD-L1, and MSI needs to be done in frontline therapy. The good thing is that all of those can be done relatively quickly, mostly using immunohistochemistry. HER2 often needs reflective fish testing, but local laboratory studies can do that. PD-L1 is straightforward to do, and MSI is straightforward to do all using immunohistochemistry. The testing can be quick. The turnaround time is quick. If you have adequate tissue sample, I encourage broader molecular testing than those 3 markers, as we often do uncover other molecular abnormalities that may play in either first line or even later lines of therapy.

This transcript has been edited for clarity.