A Phase III, Randomized, Double-Blind, Placebo-Controlled Clinical Trial to Evaluate the Efficacy and Safety of Adjuvant Atezolizumab or Placebo and Trastuzumab Emtansine for HER2-Positive Breast Cancer at High Risk of Recurrence Following Preoperative Therapy

• HER2 positive invasive breast cancer
• Stage at disease presentation: any cT2-4, any cN1-3, M0
  • Patients with cT1-3N0-1/M0 at presentation must have pathologic evidence of residual cancer in the axilla at time of surgery
  • Patients with T4 or N2-3 disease must have pathologic evidence of residual cancer in either the breast and/or the axilla
• Completion of at least 6 cycles and 16 weeks of pre-operative systemic chemotherapy including 9 weeks of a taxane and 9 weeks of trastuzumab
• Cannot have had a best response to neoadjuvant therapy of progressive disease
• < or = 12 weeks since primary surgery and randomization
• ECOG PS 0-1
• LVEF >or = 50%
• No prior T-DM1 or immune checkpoint inhibitors
• Documentation of PD-L1 status

• Primary:
  • Invasive disease-free survival
• Secondary:
  • IDFS including second primary non-breast cancer
  • DFS
  • OS
  • Distant Recurrence-Free Survival
  • PROs
  • Safety