Microsatellite instability-high or MSI-high is a genetic condition where the chances of mutations are high, and if someone has cancer, their cells have a high number of mutations. It’s also called MSI-H cancer. The microsatellite testing is done to figure out how many mutations are present. 30% or more means it’s microsatellite instability-high.

Microsatellites are basically short, recurring DNA sequences. When cancer cells have microsatellite instability-high, their cells can not correct any mistakes that might occur when DNA is being copied.

Microsatellite instability is usually found in colon cancer, endometrial cancer, and gastric cancer. It’s important to know if the cancer is microsatellite instability-high for the best possible procedure and treatment.


The human body has a repair system. It’s called DNA mismatch repair or MMR. When this system is impaired or defective, the body stops repairing and correcting any errors in DNA copying. These errors contribute to the accumulated mutations in cells and result in the tumor becoming unstable.

Doctors do a tissue biopsy followed by surgery which tests the tumor to see if it is MSI-high. MSI-high cancer cells are abnormal in every way, in their shape and behavior. However, for colon cancer, this helps in identifying these cells as most cancer cells remain undetected in the immune system.

Lynch Syndrome and MSI-High

According to a 2016 study, 15% of color cancers have tumors that are MSI-high. And this is connected to a hereditary disorder known as Lynch Syndrome. 3% of these MSI-high colon cancers are associated with this syndrome.

People who have “lynch syndrome” usually have a higher risk of developing cancer, especially colon cancer. MSI-H is the symbol of lynch syndrome in a tumor or cancer cell. MSI screening or DNA analysis is done to test normal and cancer/tumor tissues. When the result is different for both, the tumor is declared as microsatellite instability-high.

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