PDCD1 and metastatic melanoma: After the introduction of immunotherapy the average life expectancy for a patient with metastatic melanoma, ranging from six to twelve months before, has definitely improved: in patients treated with anti–PD-1 alone or in combination with ipilimumab the 3-year overall survival (OS) exceed 50% [57], reaching 35–40% at 5 years for anti–PD-1 alone [58] and over 50% at 6.5 years for nivolumab plus ipilimumab [59].