week5 importance of genetic testing in GI cancer

I'm Chengqi Xu. This week I've done a good amount of background literature reading to better understand why it's very important to conduct genetic testing for GI cancer patients. Dr. Manish Shah recently discusses the importance of genetic testing in gastrointestinal (GI) cancer. 

Dr. Shah addresses it is important to conduct genetic testing for patients with GI cancer as soon as they're diagnosed. Lack of access to adequate tissue and the time needed for testing adds to the importance of testing as soon as possible, since treatments can vary depending on the presence of actionable biomarkers.

HER2-positive GI cancer differs from that of HER2-positive breast cancer in that the expression is more heterogeneous. Typically, oncologists begin with immunohistochemistry to determine HER2 status. Dr. Shah explains if a patient tests IHC 3+, they are considered HER2-positive. If a test returns as IHC 2+, then patients should receive a FISH test to confirm HER2 positivity. It is also important to test for mismatch repair deficiency, and if testing is done using a next-generation panel, patients should also receive microsatellite instability testing.



















Furthermore, Dr. Shah says it is important to test for PD-L1 status by IHC, and a patient’s PD-L1 combined positive score can also aid treatment decisions. Notably, pembrolizumab (Keytruda) is approved for the treatment of patients with a tumor mutational burden of 10 or higher, so evaluating that with testing is also critical. 

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