A Study of Subcutaneous Nivolumab + Relatlimab Fixed-dose Combination (FDC) in Previously Untreated Metastatic or Unresectable Melanoma

The purpose of this study is to demonstrate that the study drug exposure level of the nivolumab + relatlimab FDC subcutaneous (SC) formulation is not worse than nivolumab + relatlimab FDC intravenous (IV) administration in participants with previously untreated metastatic or unresectable melanoma.

Inclusion Criteria * Participants must have an Eastern Cooperative Oncology Group (ECOG) performance status of ≤ 1/Lansky Performance Score ≥ 80% for adolescents (≥ 12 to \< 18 years of age). * Participants must have histologically confirmed Stage III (unresectable) or Stage IV (metastatic) melanoma, per the American Joint Committee for Cancer (AJCC) staging system. * Participants must have measurable disease by computed tomography (CT) or magnetic resonance imaging (MRI) per Response Evaluation Criteria in Solid Tumors version 1.1 (RECIST v1.1). * Participants must be ≥ 12 years of age. Participants who are ≥ 12 years of age and \< 18 years of age (adolescents) must weigh ≥ 40 kg at the time of signing the informed consent (assent). * Participants must have histologically confirmed Stage III (unresectable) or Stage IV (metastatic) melanoma, per the AJCC staging system (8th edition). Exclusion Criteria * Participants must not have ocular melanoma. * Participants must not have a history of myocarditis, regardless of etiology. * Participants must not have a condition requiring systemic treatment with either corticosteroids (\>10 milligrams \[mg\] daily prednisone equivalent) or other immunosuppressive medications within 14 days of start of study treatment. Inhaled or topical steroids, and adrenal replacement steroid doses \>10 mg daily prednisone equivalent, are permitted in the absence of active autoimmune disease. * Other protocol-defined Inclusion/Exclusion criteria apply.