A Phase III, Double-Blind, Placebo-Controlled, Randomized Study of Taselisib Plus Fulvestrant Versus Placebo Plus Fulvestrant in Postmenopausal Women With Estrogen Receptor-Positive and HER2-Negative Locally Advanced or Metastatic Breast Cancer Who Have Disease Recurrence or Progression During or After Aromatase Inhibitor Therapy

This international, multicenter, randomized, double-blinded, placebo-controlled study is
designed to compare the efficacy and safety of taselisib + fulvestrant with that of placebo +
fulvestrant in postmenopausal women with estrogen receptor (ER)-positive, human epidermal
growth factor receptor-2 (HER2)-negative, oncogene that encodes for
phosphatidylinositol-4,5-bisphosphate 3-kinase (PIK3CA)-mutant, unresectable, locally
advanced or metastatic breast cancer after recurrence or progression during or after an
aromatase inhibitor (AI) therapy. There will be a 2:1 randomization to the taselisib arm
versus the placebo arm. Enrollment will be enriched for participants with PIK3CA mutant
tumors via central testing. The anticipated duration of the study is approximately 3.5 years.