STING1 and melanoma: It has been demonstrated that intratumoral administration of exogenous cGAMP or STING agonist (cyclic diguanylate monophosphate; c-di-GMP) increases endothelial STING expression and IFN-β release and strongly boosts antitumor immunity leading to control of tumor growth in a mouse model of melanoma, breast cancer and glioma (87, 89–92).