As a result of PIK3CA-related drug development, the first selective inhibitor of PI3K p110α, alpelisib, was approved by the US Food and Drug Administration (FDA) in 2019 as treatment for PIK3CA-mutated hormone receptor positive/human epidermal growth factor receptor 2 negative (HR + /HER2-) breast cancer in combination with the estrogen receptor antagonist fulvestrant in post-menopausal women and men. This evidence concerns the gene ESR1 and breast cancer.