Biomarker
MSI-H/dMMR
Also known as: Microsatellite instability, Mismatch repair deficiency, MSI-high
Definition
Microsatellite instability-high (MSI-H) or mismatch repair deficient (dMMR) tumors have defects in DNA repair mechanisms, making them highly responsive to immunotherapy.
Detailed Explanation
MSI-H/dMMR tumors accumulate many mutations due to faulty DNA mismatch repair. This creates numerous neoantigens that the immune system can recognize. These tumors are highly responsive to checkpoint inhibitors regardless of cancer type. Pembrolizumab was the first drug approved for any solid tumor based on a biomarker (MSI-H/dMMR) rather than tumor location.