A Study of Multiple Immunotherapy-Based Treatment Combinations in Hormone Receptor (HR)-Positive Human Epidermal Growth Factor Receptor 2 (HER2)-Negative Breast Cancer

Exclusion Criteria

• •Significant or uncontrolled comorbid disease as specified in the protocol
• •Uncontrolled tumor-related pain
• •Autoimmune disease except for stable/controlled hypothyroidism, Type 1 diabetes mellitus, or certain dermatologic conditions
• •Positive human immunodeficiency virus test
• •Active hepatitis B or C
• •Active tuberculosis
• •Severe infection within 4 weeks and/or antibiotics within 2 weeks prior to study treatment
• •Prior allogeneic stem cell or solid organ transplantation
• •History of malignancy other than breast cancer within 2 years prior to screening except those with negligible risk of metastasis/death
• •History of or known hypersensitivity to study drug or excipients
• •For patients entering Stage 2, recovery from all immunotherapy-related adverse events to Grade 1 or better or to baseline at the time of consent
• •Prior fulvestrant or cytotoxic chemotherapy for metastatic breast cancer, or certain other agents as specified in the protocol
• •Unresolved AEs from prior anti-cancer therapy
• •Eligibility only for the control arm
• •Prior treatment with inhibitors as specified in the protocol
• •Unacceptable toxicity with atezolizumab during Stage 1
• •Uncontrolled cardiovascular disease or coagulation disorder, including use of anticoagulants as specified in the protocol
• •Significant abdominal or intestinal manifestations within 6 months prior to treatment
• •Grade 2 or higher proteinuria