PDCD1 and colorectal cancer: Monoclonal antibodies specific for PD-1 (nivolumab, pembrolizumab), and PD-L1 (durvalumab, atezolizumab, and avelumab) have proven to be clinically effective and gained FDA approval across a wide range of cancers, such as skin cancer, lung cancer, Hodgkin lymphoma, renal cell carcinoma (RCC), head and neck cancer, bladder cancer, colorectal cancer, liver cancer, gastric cancer, triple negative breast cancer, and cervical cancer (18, 19).