PDCD1 and colorectal carcinoma: Specifically, the results from a phase Ia/Ib study of an anti-CTLA-4 monoclonal antibody, plus an anti-PD-1 antibody in metastatic microsatellite stable (MSS) CRC yielded an objective response rate of 22% [47], while previous clinical studies had shown that MSS CRC did not benefit much from immunotherapy as a single agent [48].