PDCD1 and neoplasm: Despite the fact that the therapeutic efficacy of targeting the PD-1/PD-L1 axis has been shown in patients with melanoma, non-small cell lung cancer (NSCLC), and renal cell carcinoma [12,13], there is accumulating evidence suggesting that PD-L1 can facilitate tumor resistance, and promote tumor growth and survival against traditional cancer therapies and immunotherapy [14,15].