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

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 \* 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