A Study of GDC-0810 Versus Fulvestrant in Postmenopausal Women With Advanced or Metastatic Breast Cancer Resistant to Aromatase Inhibitor (AI) Therapy

A Phase II, Open-Label, Randomized Study of GDC-0810 Versus Fulvestrant in Postmenopausal Women With Advanced or Metastatic ER+ /HER2- Breast Cancer Resistant to Aromatase Inhibitor Therapy

The primary purpose of this study is to evaluate the efficacy, safety, and tolerability of GDC-0810 compared with fulvestrant in postmenopausal women with advanced or metastatic estrogen receptor positive (ER+)/ human epidermal growth factor receptor 2 negative (HER2-) breast cancer resistant to AI therapy. The development of GDC-0810 has been halted by the Sponsor and the enrollment in this study has been discontinued. Participants currently enrolled in the study who are experiencing clinical benefit may continue receiving GDC-0810 as a single agent or fulvestrant until disease progression (PD), unmanageable toxicity, withdrawal of consent, exhaustion of GDC-0810 drug supply, or termination of the study by the Sponsor.

Inclusion Criteria:

• Postmenopausal women with histologically or cytologically confirmed invasive, ER+/HER- (defined by local guidelines) metastatic or inoperable, locally advance breast cancer
• Participants for whom endocrine therapy is recommended and treatment with cytotoxic chemotherapy is not indicated at time of entry into the study
• Participants must have measurable disease by RECIST v1.1 or non-measurable, evaluable disease with atleast one evaluable bone lesion by RECIST v1.1 based on radiologic scans within 28 days of Day 1 of Cycle 1
• Participants with radiologic/objective evidence of breast cancer recurrence or progression while on or within 6 months after the end of adjuvant treatment with an AI, or progression while on or within 1 month after the end of prior AI treatment for locally advanced or metastatic breast cancer

Exclusion Criteria:

• HER2-positive disease
• Prior treatment with fulvestrant
• Prior treatment with greater than (>) 1 cytotoxic chemotherapy regimen or >2 endocrine therapies for advanced or metastatic disease