The purpose of this study is to evaluate the efficacy of immunotherapy in the first-line treatment of metastatic melanoma in Slovenia and to investigate the association between PD-L1 expression and treatment response. The study aims to determine the relationship between exosomal PD-L1 miRNA expression, PD-L1 expression in tumor tissue, and PD-L1 expression on the surface of immune cells, and response to immunotherapy. The study will also evaluate the association between immune-related adverse events and survival.