Although the majority of GI tumors do not have the MSI-H/dMMR biomarker, its presence could lead to an immunotherapy treatment option. Every colorectal cancer and newly diagnosed gastric cancer patient should be tested for MSI-H/dMMR regardless of stage.
Each person’s DNA carries codes and sequences called microsatellites (MSI). These sequences can give a lot of information and are seen as genetic markers.
The body is always making new cells, and sometimes there are errors. Usually, there’s a set of genes that can identify and fix the errors. They are called mismatch repair genes (MMR), and they work a lot like spellcheck. When mismatch repair genes are working, the microsatellites are considered stable (MSS) and the MMR genes are proficient (pMMR).
When the MMR genes aren’t working, this is considered mismatch repair deficient (dMMR). In this case, the “spell check” is broken. This can lead to instability in the microsatellites and is called MSI-H.
Most often, solid tumor tissue is used for MSI-H/dMMR biomarker testing; however, next generation sequencing (NGS) has made liquid biopsy (blood) an alternative option when tissue is unavailable.
Many times, cancer is challenging to treat because cancer cells disguise themselves as normal cells. But tumors with MSI-H/dMMR are easier targets for immunotherapy. Immunotherapy uses the body’s immune system to fight cancer by turning “off” certain proteins that stop immune cells from attacking abnormal cells.
The following immunotherapy drugs may be recommended for patients with MSI-H/dMMR tumors. Each treatment plan depends on your stage, line of treatment, surgical or additional treatment options, and your overall health.
All GI cancers (in advanced, specific situations)
Only colon and rectal cancers (in advanced, specific situations)
You may be given only immunotherapy or a combination of immunotherapy and chemotherapy drugs.
Ask your doctor how your biomarker test results are informing your treatment plan and if you qualify for any clinical trials.
