The addition of the CDK4/6 inhibitors palbociclib, ribociclib, and abemaciclib to an aromatase inhibitor were studied in postmenopausal HR‐positive/HER2‐negative advanced breast cancer in the first‐line setting in PALOMA‐2, MONALEESA‐2, and MONARCH‐3 trials, respectively. Here, CYP19A1 is linked to breast cancer.