CD274 and small cell lung carcinoma: Anti-PD-L1 mAbs, i.e., atezolizumab, durvalumab, and avelumab, are approved for the treatment of melanoma, NSCLC, small cell lung cancer (SCLC), HCC, urothelial carcinoma, biliary tract cancers (BTC), and metastatic Merkel cell carcinoma (MCC) [60,61,62].