Among the mechanisms responsible for resistance to immunotherapy, metabolism seems to play a major role. A better understanding of tumor metabolism appears to be absolutely necessary in order to propose efficient therapeutic alternatives to target tumor cells without exerting a deleterious effect on the cells responsible for the anti-tumor immune response. The main objective is to evaluate metabolism modulations in melanoma cells extracted from metastases of patients sensitive and resistant to immunotherapies (anti-PD1 or anti-PD1+anti-CTLA4).

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.