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

A Phase Ib, Open-Label, Multicohort Study of the Safety, Efficacy, and Pharmacokinetics of Tiragolumab in Combination With Atezolizumab and Chemotherapy in Patients With Triple-Negative Breast Cancer

The purpose of this study is to evaluate the safety, efficacy, and pharmacokinetics of tiragolumab in combination with atezolizumab and chemotherapy in participants with metastatic and early triple-negative breast cancer (TNBC).

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