A Study Evaluating the Efficacy and Safety of Multiple Treatment Combinations in Patients With Metastatic or Locally Advanced Breast Cancer

Inclusion Criteria

• Inclusion Criteria Patients must meet all of the following criteria to qualify for Stage 1 (all cohorts) and to qualify for Stage 2 (2L CIT-naïve cohort): - Age >/= 18 years at the time of signing Informed Consent Form - ECOG Performance Status of 0 or 1 - Able to comply with the study protocol, in the investigator's judgment - Metastatic or inoperable locally advanced breast cancer - Measurable disease (at least one target lesion) according to RECIST v1.1 - Life expectancy >/= 3 months, as determined by the investigator - Tumor accessible for biopsy, unless archival tissue is available - Availability of a representative tumor specimen that is suitable for biomarker analysis via central testing - Adequate hematologic and end-organ function, defined by the following laboratory test results, obtained within 14 days prior to initiation of study treatment - For women of childbearing potential: agreement to remain abstinent (refrain from heterosexual intercourse) or use contraceptive measures and agreement to refrain from breastfeeding and donating eggs, as outlined for each specific treatment arm - For men: agreement to remain abstinent (refrain from heterosexual intercourse) or use contraceptive measures, and agreement to refrain from donating sperm, as outlined for each specific treatment arm Exclusion Criteria for Stage 1 - Prior treatment with T-cell co-stimulating or immune checkpoint blockade therapies, including anti-CTLA-4, anti-PD-1, and anti-PD-L1 therapeutic antibodies, CD40 agonists or interleukin-2 (IL-2) or IL-2-like compounds - Treatment with investigational therapy within 28 days prior to initiation of study treatment - Biologic treatment (e.g., bevacizumab) within 2 weeks prior to initiation of study treatment, or other systemic treatment for TNBC within 2 weeks or 5 half-lives of the drug (whichever is longer) prior to initiation of study treatment - Adverse events from prior anti-cancer therapy that have not resolved to Grade </= 1 or better with the exception of alopecia of any grade and Grade </= 2 peripheral neuropathy - Eligibility only for the control arm Exclusion Criteria for Stage 1 (both cohorts) and Stage 2 (2L CIT-naïve cohort) - Uncontrolled pleural effusion, pericardial effusion, or ascites requiring recurrent drainage procedures (once monthly or more frequently) - Uncontrolled tumor-related pain - Symptomatic, untreated, or actively progressing central nervous system (CNS) metastases - History of leptomeningeal disease - Active or history of autoimmune disease or immune deficiency - History of idiopathic pulmonary fibrosis, organizing pneumonia (e.g., bronchiolitis obliterans), drug-induced pneumonitis, or idiopathic pneumonitis, or evidence of active pneumonitis on screening chest computed tomography (CT) scan. History of radiation pneumonitis in the radiation field (fibrosis) is permitted. - Active tuberculosis - Severe infection within 4 weeks prior to initiation of study treatment - Treatment with therapeutic oral or IV antibiotics within 2 weeks prior to initiation of study treatment - Significant cardiovascular disease - Prior allogeneic stem cell or solid organ transplantation - History of malignancy other than breast cancer within 2 years prior to screening, with the exception of those with a negligible risk of metastasis or death - Treatment with systemic immunosuppressive medication (including, but not limited to, corticosteroids, cyclophosphamide, azathioprine, methotrexate, thalidomide, and anti-tumor necrosis factor alpha agents) within 2 weeks prior to initiation of study treatment, or anticipation of need for systemic immunosuppressive medication during the course of the study - Pregnancy or breastfeeding, or intention of becoming pregnant during the study