Sara Tolaney, MD, Dana Farber Cancer Institute, Boston, MA, evaluates the use of CDK4/6 inhibitors in early stage hormone-receptor (HR)-positive, HER2-negative breast cancer, of which conflicting results have been reported. monarchE (NCT03155997), evaluating abemaciclib, resulted in a significant improvement in invasive disease-free survival, however, PALLAS (NCT02513394) and PENELOPE-B (NCT01864746) did not result in benefit from the use of adjuvant palbociclib. This interview took place at the virtual European Society for Medical Oncology (ESMO) Breast Cancer Congress 2021.