ERBB2 and breast cancer: It is indicated in combination with fulvestrant for the treatment of postmenopausal women and men with HR-positive, HER2-negative, PIK3CA-mutated, advanced, or metastatic breast cancer as detected by an FDA-approved test following progression on or after an endocrine-based regimen.393 This is also the first PI3K inhibitor approved for clinical treatment of breast cancer.