PDCD1 and melanoma: Recent data suggests, that PD-L1 testing by immunohistochemistry prior to immunotherapy may be used to  select patients who will most likely respond to therapy with PD-L1 inhibitors [19, 20] and has therefore been approved as companion diagnostic tests for therapeutic anti-PD-1 antibodies in lung, kidney and urothelial carcinoma, as well as in malignant melanoma [6–8, 20].