PDCD1 and neoplasm: Interestingly, the combination of cGAMP with radiation or blockade of PD-1/PD-L1 and CTLA-4 produces synergistic anti-tumor effects, which indicates that the cGAS–STING pathway is important for the sensing of cancer cells by the innate immune system (40, 61, 115) generating local and systemic anti-cancer immune responses (40, 42, 98, 124–130) and numerous clinical trials are ongoing (Clinicaltrials.gov study identifiers: NCT02675439; NCT03172936).