PDCD1 and cancer: In the past decade, immune checkpoints inhibitors (ICIs) have emerged as anticancer agents targeting inhibitory receptors (e.g. CTLA-4, PD-1, LAG-3, TIM-3) and ligands (PD-L1) expressed on T lymphocytes, antigen presenting cells and tumor cells and elicit an anti-tumor response by stimulating immune system and dramatically improved prognosis of many cancer patients including NSCLC patients [33].