MSH6 and neoplasm: MMR-d (per MLH1, MSH2, MSH6, and PMS2 immunohistochemistry (IHC) negative staining, or microsatellite instability assessment); PD-L1 expression; and tumor mutational burden (TMB) (when available) [1, 29] are the most common biomarkers being used in practice, with various degrees of success for patient selection.