ERBB2 and breast cancer: Abemaciclib is a potent, selective small‐molecule CDK4/6 inhibitor and is FDA‐approved as monotherapy and in combination with endocrine therapy for hormone receptor positive (HR+) and human epidermal growth factor receptor 2 negative (HER2‐) advanced breast cancer,23, 24, 25 and for the adjuvant treatment of HR+, HER2‐, node‐positive, early breast cancer at high risk of recurrence.26, 27