Inclusion Criteria: - ≥ 18 years - advanced melanoma (Stage III/Stage IV) - histologically confirmed diagnosis - treatment decision for nivolumab mono- or combination therapy already taken - primary diagnosis of advanced melanoma after complete surgical tumor resection and no evidence of disease (cohort 3 only) Exclusion Criteria: - current primary diagnosis of a cancer other than advanced melanoma, that requires systemic or other treatment - previous treatment with nivolumab, for nivolumab monotherapy cohort only - current active participation in an interventional clinical trial for treatment of advanced melanoma - Patients with a current diagnosis of persisting advanced melanoma or a cancer other than advanced melanoma that requires systemic or other treatment or has not been treated curatively (as per discretion of the investigator) (cohort 3 only)