B2M truncating mutations were recently discovered in melanoma, resulting in loss of surface expression of major histocompatibility complex (MHC Class I) [56], and loss of such MHC Class I-mediated antigen presentation frequently recognized in MMR-deficient colon cancer rendered these tumors resistant to CTL-mediated tumor immunity [57]. The gene discussed is B2M; the disease is malignant colon neoplasm.