A Study Evaluating the Efficacy and Safety of Multiple Immunotherapy-Based Treatment Combinations in Patients With Metastatic or Inoperable Locally Advanced Triple-Negative Breast Cancer

Open to people ages 18 years and up

Stage 1

- Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 or 1 - Metastatic or inoperable locally advanced, histologically documented TNBC (absence of HER2, ER, and PR expression) - For the 1L PD L1+ cohort: no prior systemic treatment for metastatic or inoperable locally advanced TNBC - For the 2L CIT-naive cohort: Eligible for capecitabine monotherapy - For the 2L CIT-naive cohort: Radiologic/objective evidence of recurrence or disease progression after 1L treatment with chemotherapy, for a total of one line of therapy for inoperable locally advanced or metastatic breast cancer - Life expectancy =/> 3 months, as determined by the investigator - Tumor accessible for biopsy - Availability of a representative tumor specimen that is suitable for determination of PD-L1 and/or additional biomarker status via central testing - For the 1L PD L1+ cohort: Positive PD-L1 expression, defined as >/= 1% of the tumor area occupied by PD L1-expressing tumor-infiltrating immune cells of any intensity, as determined through use of the U.S. Food and Drug Administration-approved or CE-marked Ventana PD-L1 (SP142) Assay Inclusion Criteria for Stage 1 (both cohorts) and Stage 2 (2L CIT-naive cohort) - Measurable disease (at least one target lesion) - Adequate hematologic and end-organ function, laboratory test results, obtained within 14 days prior to initiation of study treatment. - Negative HIV test at screening - Negative hepatitis B surface antigen test - Negative total hepatitis B core antibody (HBcAb) - Negative hepatitis C virus (HCV) antibody test at screening - 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 Inclusion Criteria Stage 2 (2L CIT-naive cohort) - ECOG Performance Status of 0, 1, or 2 - Patients randomly allocated to the control arm during Stage 1: ability to initiate Stage 2 treatment within 3 months after experiencing unacceptable toxicity, provided that Medical Monitor approval for entry into Stage 2 is obtained, or disease progression per RECIST v1.1 while receiving control treatment - Patients randomly allocated to an experimental arm during Stage 1: ability to initiate Stage 2 treatment within 3 months after experiencing unacceptable toxicity not related to atezolizumab, disease progression per RECIST v1.1, or loss of clinical benefit as determined by the investigator while receiving Stage 1 treatment - Availability of a tumor specimen from a biopsy performed upon discontinuation of Stage 1 (if deemed clinically feasible by the investigator)

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 Exclusion Criteria for the 2L CIT-naive cohort, Stage 1 - Prior treatment with capecitabine, - Treatment with sorivudine or its chemically related analogues, such as brivudine - History of severe and unexpected reactions to fluoropyrimidine therapy - Known complete absence of dihydropyrimidine dehydrogenase activity Exclusion Criteria for Stage 2 - Inability to tolerate atezolizumab during Stage 1 - For patients receiving eribulin: congenital long QT syndrome Additional drug-specific exclusion criteria may apply to Stage 1 and 2