A Phase II Randomized, Double-Blind Study of Neoadjuvant Letrozole Plus GDC-0032 Versus Letrozole Plus Placebo in Postmenopausal Women With ER-positive/HER2-negative, Early Stage Breast Cancer

This is a two-arm, randomized, double-blind, multicenter, pre-operative study to evaluate the effect of combining letrozole and GDC-0032 (also known as taselisib) versus letrozole and placebo in postmenopausal women with estrogen receptor-positive (ER+)/human epidermal growth factor receptor 2 (HER2) untreated, Stage I-III operable breast cancer. Participants will be randomized into one of the two treatment arms with a 1:1 randomization ratio. Letrozole at 2.5 milligrams (mg) will be dosed once daily plus either Taselisib at 4 mg (two 2-mg tablets) or placebo on a 5 days-on/ 2 days-off schedule for a total of 16 weeks.