CD274 and small cell lung carcinoma: Activation of the cGAS-STING pathway has been demonstrated to increase the expression of PD-L1 on the surface of tumor cells and thus attenuate the activity of CTLs, which has been confirmed in models of liver cancer (64), melanoma (65), non-small cell lung cancer (NSCLC) (16) and small cell lung cancer (SCLC) (46, 66).