PDCD1 and colorectal cancer: However, while immune checkpoint blockade antibodies, such as those against programmed cell death-1 (PD-1) or cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), have shown remarkable efficacy in certain cancer types such as melanoma and non-small-cell lung carcinoma (3, 4), limited therapeutic benefit has been also observed in other types of cancers such as colorectal cancer, ovarian cancer, and pancreatic ductal adenocarcinoma.