PDCD1 and cancer: Up to now, PD-L1/PD-1 immune cell interaction has been defined as canonical signaling, characterized by high infiltration of CD8+ T cells and conventional CD4+ T cells, while recent studies found that PD1 non-canonical via, inhibits proliferation of cancer cell via suppressing AKT and ERK signaling hence it plays an important role in tumorigenesis, suggesting that should be a potential therapeutic strategy.