PDCD1 and cancer: Targeting immune-checkpoint molecules, such as programmed cell death 1 (PD-1), programmed cell death ligand 1 (PD-L1) and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), has also demonstrated to be one of the most promising cancer treatments, with positive results in KRAS-mutated cancers [133,134].