B2M and colorectal carcinoma: Another overriding immune escape mechanism is the evidence for mutations in a microsatellite region of β2-microglobulin (B2M) gene which forms an essential component of the (neo)antigen presentation machinery of the MHC class I protein with the mutation leading to total loss of HLA expression observed in nearly 30% of MSI-H CRC patients [95,96,97].