PDCD1 and metastatic melanoma: It has redefined treatment guidelines for most forms of cancer, especially for drugs that are effective on the programmed cell death protein 1/programmed cell death ligand 1 (PD-1/PD-L1) signaling pathway, since nivolumab has been approved by the National Health System for the treatment of metastatic melanoma and second-line therapy of non-small cell lung cancer (NSCLC) (16, 17).