For more information regarding Bristol-Myers Squibb Clinical Trial participation, please visit www.BMSStudyConnect.com Inclusion Criteria: - Histological and cytological confirmation of adenocarcinoma of the breast - Documented HER2 negative and estrogen receptor (ER) positive status of primary or metastatic tumor tissue using the most recently assessed tumor specimen, according to the local laboratory parameters - ER negativity is defined as < 1% of tumor cells expressing hormonal receptors via IHC analysis - At least one measurable lesion, as per Response Evaluation Criteria in Solid Tumors version 1.1 [RECIST v1.1] that can be accurately assessed at baseline and is suitable for repeated assessment by computed tomography (CT) or magnetic resonance imaging (MRI) - Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1 - Women and Men must agree to follow specific methods of contraception, if applicable, while participating in the trial Exclusion Criteria: - Allergy or hypersensitivity to any study drugs or their excipients - Any other sound medical, psychiatric and/or social reason as determined by the investigator - Active, known, or suspected autoimmune disease or immune-related diseases - History of unstable or deteriorating cardiac disease within the previous 12 months prior to screening - Prior therapy with anti-programmed death 1 (PD-1), anti-programmed death-ligand 1 (PD-L1) or anti-Cytotoxic T Lymphocyte Antigen 4 (CTLA-4) class antibody - Any major surgery within 4 weeks of the first dose of study treatment Other protocol-defined inclusion/exclusion criteria apply