MRC1 and colorectal carcinoma: In CRC, immune checkpoint inhibitors (ICIs) targeting the PD-1/PD-L1 axis have gained approval for use exclusively in tumors exhibiting mismatch repair deficiency (MMR-D) and high microsatellite instability (MSI-H), which are associated with mutations in DNA mismatch repair (MMR) genes, present in approximately 15% of CRC cases [110].