
Microsatellite instability has been an FDA-indicated biomarker for immunotherapy since 2017, when the PD-1 inhibitor pembrolizumab was approved for patients with solid tumors found to be mismatch repair deficient or MSI high. Other approvals since then, such as for the combination of ipilimumab and nivolumab in patients with MSI-H/dMMR metastatic colorectal can­cer, have established the relevance of cancer thera­pies for tumors with this biomarker specifically rather than tumor histology alone.








