Patients aged over 18 years with an established diagnosis of MM who are treated and followed up at the Department of Dermatology are asked to participate in the study after the indication for treatment with ipilimumab is given by the interdisciplinary skin tumorboard conference. After written informed consent is obtained, patients undergo a baseline evaluation (V1) including a medical history, physical examination, laboratory analyses (hemoglobin, leucocytes count, C-reactive protein, and pulmonary function tests (PFTs) with spirometry and measurement of DLCO. Thereafter, the first dose of ipilimumab (3mg/kg) is given intravenously over a period of 90 minutes without premedication. The subsequent three doses of ipilimumab are administered three weekly with analogue dose. Subsequent study visits (V2, V3, V4) including PFTs are scheduled on the same day as ipilimumab is administered. Thus, study visits are thoroughly adapted to the clinical visits, which is given by the administration of ipilimumab (total of four injections each separated by three weeks). In case of new respiratory symptoms during the study period, additional PFTs and a high-resolution computed tomography (HR-CT) of the chest are performed. In case of early study termination during follow-up pulmonary function test values which are already obtained are used for the final analysis.