A Study of the Safety, Efficacy, and Pharmacokinetics of Tiragolumab in Combination With Atezolizumab and Chemotherapy in Participants With Triple-Negative Breast Cancer

Inclusion Criteria

• Inclusion Criteria Cohort A: - Metastatic or locally advanced unresectable, histologically documented TNBC characterized by absence of human epidermal growth factor 2 (HER2), estrogen receptor (ER), and progesterone receptor (PR) expression - Only patients with metastatic TNBC tumors that are centrally tested and found to be programmed death-ligand 1 (PD-L1) positive will be enrolled - No prior chemotherapy or targeted systemic therapy for inoperable locally advanced or metastatic TNBC - Eastern Cooperative Oncology Group performance status of 0 or 1 - Measurable disease, as assessed by the investigator according to RECIST v1.1 - Adequate hematologic and end-organ function Cohort B: - Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1 - Histologically documented TNBC (negative HER2, ER, and PR status) - Confirmed tumor PD-L1 evaluation as documented through central testing of a representative tumor tissue specimen - Primary breast tumor size of greater than (>) 2 centimeters (cm) by at least one radiographic or clinical measurement - Stage at presentation: cT2-cT4, cN0-cN3, cM0 - Baseline left ventricular ejection fraction (LVEF) greater than or equal to (>/=) 53 percent (%) measured by echocardiogram (ECHO) or multiple-gated acquisition (MUGA) scans - Adequate hematologic and end-organ function Exclusion Criteria Cohort A: - Formalin-fixed, paraffin-embedded (FFPE) tumor tissue that is PD-L1 negative, as determined on the SP142 PD-L1 immunohistochemistry assay, with positivity defined as immune cells greater than or equal to (>/=) 1% - Spinal cord compression not definitively treated with surgery and/or radiation or previously diagnosed and treated spinal cord compression without evidence that disease has been clinically stable for >2 weeks prior to initiation of study treatment - Known central nervous system (CNS) disease, except for treated asymptomatic CNS metastases - Leptomeningeal disease Cohort B: - History of invasive breast cancer - Stage IV (metastatic) breast cancer - Prior systemic therapy for treatment and prevention of breast cancer - Previous therapy with anthracyclines, platinum, or taxanes for any malignancy - Synchronous, bilateral invasive breast cancer - Cardiopulmonary dysfunction