PDCD1 and colorectal carcinoma: Thus, due to the expression of the immunosuppressive molecules blocking antitumor immunity, programmed cell death-1 (PD-1) and cytotoxic T lymphocyte-associated protein 4 (CTLA-4), on the surface of activated immune cells, the immune checkpoint inhibitors, anti-PD-1 such as pembrolizumab and nivolumab, and anti-CTLA-4 antibodies ipilimumab were also approved by FDA only for patients with microsatellite instability-high/mismatch repair deficient (MSI-H/MMR-D) mCRC and exhibited multiple efficacies in CRC patients (Myint and Goel, 2017).