dMMR/MSI-H CRC have been determined to exhibit a higher tumor mutation burden than pMMR/MSS CRC and more tumor infiltrating lymphocytes (TILs) with activated CD8+ cytotoxic T-lymphocyte (CTL) and T helper type 1 (Th1) cells characterized by IFN-γ production: making these tumors sensitive to treatment with immune checkpoint inhibitors (ICIs), like anti-PD-1 (Programmed cell death protein 1, CD279) and anti-PD-L1 (Programmed Death Ligand 1, CD274) inhibitors (6–9). The gene discussed is CD8A; the disease is neoplasm.