The “Perioperative Endocrine Therapy_ Individualizing Care (POETIC)” phase III trial randomly allocated 4486 postmenopausal ER+ HER2- breast cancer patients to peri-operative aromatase inhibitor (POAI) for 14 days before and 14 days after surgery vs. no peri-operative treatment. The gene discussed is ESR1; the disease is breast carcinoma.