A phase III trial of alpelisib + trastuzumab ± fulvestrant versus trastuzumab + chemotherapy in HER2+ PIK3CA-mutated breast cancer.

ALPHABET is a randomized phase III trial assessing alpelisib + trastuzumab with or without fulvestrant in previously treated HER2-positive PIK3CA-mutated advanced breast cancer. Patients will be included in two cohorts according to hormone receptor (HR) status. In the experimental arms, patients in the HR-negative cohort will receive trastuzumab + alpelisib, and patients in the HR-positive cohort will receive the same treatment plus fulvestrant. Patients in the control arms will receive trastuzumab + physician's choice chemotherapy (eribuline, capecitabine or vinorelbine). Key eligibility criteria include 1-4 previous lines of anti-HER2 therapy and prior trastuzumab emtansine. The primary end point is investigator-assessed progression-free survival. The study aims to recruit a total of 300 patients.