PDCD1 and lung cancer: The development and application of antibodies targeting PD-1 (nivolumab and pembrolizumab) and PD-L1 (atezolizumab, avelumab, and durvalumab) have yielded favourable therapeutic effects on various solid tumors, such as lung cancer, melanoma, renal cell carcinoma, Hodgkin's lymphoma, urothelial cancer, head and neck cancer, gastric cancer, Merkel cell carcinoma, and mismatch repair deficiency or microsatellite instable-high solid tumors [3–6].