Cyclin-Dependent Kinase 4/6 Inhibitors as Neoadjuvant Therapy of Hormone Receptor-Positive/HER2-Negative Early Breast Cancer: What do we Know so Far?

The introduction of cyclin-dependent kinase 4/6 (CDK4/6) inhibitors to the treatment of hormone receptor-positive and human epidermal growth factor receptor 2-negative (HR + /HER2 -) metastatic breast cancer is regarded as one of the greatest achievements of the last decades in breast oncology. To date, palbociclib, abemaciclib and ribociclib are the 3 approved CDK4/6 inhibitors that combined with endocrine therapy are now considered as the standard first-line treatment of metastatic HR + /HER2 - breast cancer. The great success of these drugs in the setting of metastatic disease and the need to combat the high risk of recurrence have paved the way for a number of clinical trials to explore the use of CDK4/6 inhibitors in the neoadjuvant treatment of early breast cancer. In this review, we summarize the main findings of clinical trials that examined the use of CDK4/6 inhibitors in combination with hormone therapy or chemotherapy as neoadjuvant treatment of hormone receptor-positive and HER2-negative breast cancer. Active clinical trials that investigate different treatment schemes are also briefly presented and current limitations and future goals are discussed.