CYP19A1 and breast cancer: Based on the data of the monarchE trial investigating the CDK4/6 inhibitor abemaciclib for 2 years in the early setting, abemaciclib was approved in combination with tamoxifen or as an aromatase inhibitor for the adjuvant treatment of women with node-positive early breast cancer at high risk of recurrence (≥4 positive lymph nodes or 1–3 positive lymph nodes and either tumor grade 3 or T3-tumors or high KI67) [45].