Of 310 cancer patients treated with ICIs at Coltea Clinical Hospital, Bucharest, Romania, over a period of 5 years, we identified 1 case of breast cancer, 3 of cancer of unknown primary, 12 of renal cancer, 10 of urothelial cancer, 42 of malignant melanoma, 91 of head and neck cancer and 151 of lung cancer, respectively, treated with PD-1 inhibitor (nivolumab—142 patients, pembrolizumab—146 patients), PD-L1 inhibitor (atezolizumab—10 patients, durvalumab—2 patients, avelumab—1 patient) and CTLA-4 antibody (ipilimumab—9 patients). This evidence concerns the gene CTLA4 and melanoma.