Inclusion Criteria: - Men & women ≥ 18 years of age - Eastern Cooperative Oncology Group (ECOG) performance status (PS) 0-1 - Histologically confirmed Stage III (unresectable)/Stage IV melanoma - Measurable disease by computed tomography (CT)/magnetic resonance imaging (MRI) per Response Evaluation Criteria in Solid Tumors (RECIST) 1.1 criteria - RECIST defined disease progression during or after ≤ 2 prior treatment regimens - Pre-treatment fresh core or excision tumor biopsy. - Archival Formalin-fixed paraffin-embedded (FFPE) tumor material if available Exclusion Criteria: - Any treatment in a BMS-936558 trial - Subjects with condition requiring systemic treatment with either corticosteroids (> 10mg daily prednisone/equivalent) or other immunosuppressive medications within 14 days of study drug administration - Active, known or suspected autoimmune disease - Unknown BRAF status - Active brain metastasis or leptomeningeal metastasis - Ocular melanoma - Prior therapy with anti programmed death-1 (anti-PD-1), anti programmed death-ligand 1 (anti-PD-L1) or anti-programmed death-ligand 2 (anti-PD-L2)