For the adjuvant treatment of adults with HR-positive, HER2-negative, node-positive, early breast cancer with a high risk of recurrence and a 20% Ki-67 score, as determined by an FDA-approved test, a combination of abemaciclib and endocrine therapy (tamoxifen or an aromatase inhibitor) was advised. This was the first CDK-4/6 inhibitor approved for adjuvant treatment of breast cancer. The gene discussed is CYP19A1; the disease is breast cancer.