Targeting the cell cycle with cyclin-dependent kinase (CDK)-4/6 inhibitors such as palbociclib, ribociclib, and abemaciclib in combination with aromatase inhibitors has been shown to improve clinical outcomes in patients with advanced ER+/HER2− breast cancer (3), and has been approved as first- and second-line treatment options. The gene discussed is CYP19A1; the disease is breast carcinoma.