PDCD1 and cancer: The most commonly used cancer therapies are targeted to proteasome, vascular endothelial growth factor-VEGR and its receptor- -VEGFR, epidermal growth factor receptor- EGFR, human epidermal growth factor receptor-2-HER2, dimerizations of HER2, v-Raf murine sarcoma viral oncogene homolog B- BRAF, anaplastic lymphoma kinase-ALK, programmed cell death protein 1-PD-1 and its ligand PDL-1, receptor activator of nuclear factor kappa beta ligand- RANKL, and mammalian target of rapamycin-mTOR.