PDCD1 and lung cancer: Monoclonal antibodies targeting the CTLA-4 pathway (ipilimumab) (Rittmeyer et al., 2017), PD-1 (nivolumab and pembrolizumab) (Tanvetyanon et al., 2016), and PD-L1 (durvalumab, atezolizumab, and avelumab) (Zhou et al., 2016) have achieved promising improvements in second-line therapy for advanced lung cancers.