PDCD1 and lung cancer: Since the 2000s, the understanding of the pathogenesis of lung cancer has broadened, and now NSCLC can be classified into several subtypes according to mutations such as those involving epidermal growth factor receptor (EGFR), anaplastic lymphoma kinase (ALK), ROS proto-oncogene 1 receptor tyrosine kinase (ROS1) and programmed cell death protein 1 (PD-1).