A Study Evaluating the Efficacy and Safety of Adjuvant Atezolizumab or Placebo and Trastuzumab Emtansine for Participants With HER2-Positive Breast Cancer at High Risk of Recurrence Following Preoperative Therapy

Exclusion Criteria

• •Completion of pre-operative systemic chemotherapy including at least 9 weeks of taxane and 9 weeks of trastuzumab (anthracycline and/or additional HER2-targeted agents are permitted)
• •\<=12 weeks between primary surgery and randomization
• •Eastern Cooperative Oncology Group (ECOG) Performance Status 0 or 1
• •Screening left ventricular ejection fraction (LVEF) \>= 50% and no decrease in LVEF by \>15% from the pre-chemotherapy LVEF. If no pre-chemotherapy LVEF, screening LVEF \>= 55%
• •Life expectancy \>= 6 months
• •Adequate hematologic and end organ function
• •Stage IV breast cancer
• •An overall response of disease progression according to the investigator at the conclusion of preoperative systemic therapy
• •Prior treatment with T-DM1, or atezolizumab, or other immune checkpoint inhibitors
• •History of exposure to various cumulative doses of anthracyclines
• •History of other malignancy within 5 years prior to screening, except for appropriately treated carcinoma in situ of the cervix, non-melanoma skin carcinoma, Stage I uterine cancer, or ductal carcinoma in situ (DCIS)
• •Current grade \>=2 peripheral neuropathy
• •History of idiopathic pulmonary fibrosis, organizing pneumonia, or pneumonitis
• •History of or active autoimmune disease or immune deficiency
• •Treatment with immunostimulatory or immunosuppressive agents
• •Cardiopulmonary dysfunction
• •Any known active liver disease