CTLA4 and malignant colon neoplasm: In colon cancer, pembrolizumab and nivolumab (anti-PD1 antibodies) have been FDA approved as monotherapy or combined with ipilimumab (anti-CTLA-4 antibody) as treatment for patients with microsatellite instability high (MSI-H)/DNA mismatch repair-deficient (dMMR) mCRC.