Study of Alterations in Tumor Metabolism Associated With the Development of Immunotherapy Resistance in Melanoma

Inclusion Criteria: * Female or male, 18 years of age or older * Stage III unresectable or histologically confirmed stage IV cutaneous melanoma (melanoma of unknown origin is accepted), treatment naïve (metastatic stage) and for which immunotherapy will be started * Performance Status ≤1 * BRAF status available; BRAF status determination is required but patient will be eligible regardless of BRAF status * For women of childbearing potential, effective contraception must be initiated during the study. * Patient affiliated to social security plan * Patient having signed informed consent Exclusion Criteria: * Breastfeeding or pregnant patients: for women of childbearing age, a urine pregnancy test will be performed * Patients with ocular or mucosal melanoma of metastatic ocular melanoma * Patients with metastatic melanoma not treated with immunotherapy (i.e. treated with a combination of targeted therapies). * Contraindication to the initiation of immunotherapy: HIV and/or HCV and/or HBV positive, active autoimmune disease (chronic inflammatory bowel disease such as ulcerative colitis, Crohn's disease, vasculitis, etc.), patients with autoimmune motor neuropathy (such as Guillain Barré syndrome). * Vulnerable patients: minors, adults under guardianship or curatorship, deprived of liberty * Vulnerable persons (minors, patients under guardianship or curatorship, deprived of liberty, under court protection, etc.). * A psychiatric or addiction history that will compromise the patient's ability to consent and follow the proper protocol procedures * Any other clinical finding that, in the opinion of the principal investigator, could interfere with the results of the study or pose a risk to the patient during the study.