For this trial, 668 postmenopausal patients with metastatic HR positive (HR+), Her2-negative advanced breast cancer treated with endocrine therapy ± ribociclib were randomized 1:1 to receive either the cyclin dependent kinase (CDK)4/6 inhibitor ribociclib 600 mg per day 3 weeks on/1 week off, or placebo together with the aromatase inhibitor letrozole [8]. The gene discussed is CYP19A1; the disease is breast carcinoma.