The ongoing phase 3 CAPItello-291 trial (NCT04305496) is assessing the efficacy and safety of capivasertib plus fulvestrant versus placebo plus fulvestrant in patients with aromatase inhibitor-resistant ER-positive, HER2-negative advanced breast cancer, including those who have received previous CDK4/6 inhibitors. This evidence concerns the gene CYP19A1 and breast carcinoma.