CDK4/6 inhibitor plus endocrine therapy for hormone receptor‐positive, HER2‐negative metastatic breast cancer: The new standard of care

Patients presenting with hormone receptor‐positive (HR + ), human epidermal growth factor receptor 2‐negative (HER2 – ) metastatic breast cancer (MBC) are usually treated with endocrine therapy (ET), except if there is a concern about endocrine resistance or a need to achieve rapid disease control due to visceral crisis. The combination of CDK4/6 inhibitor + ET has now replaced single‐agent ET as the standard first‐line treatment; and it can also be considered a standard option in the second‐line setting. This review briefly summarizes recently reported efficacy findings from the key phase III clinical trials of CDK4/6 inhibitor + ET in patients with HR + /HER2 – MBC, including evidence that adding a CDK4/6 inhibitor to ET improves overall survival and does so without reducing patients’ quality of life. There is still much to learn regarding the use of CDK4/6 inhibitors and how they may be optimally integrated into clinical practice. In particular, there is a need for specific biomarkers that help predict the likelihood of response or resistance to CDK4/6 inhibitor therapy; and for data to guide treatment decisions when a patient's disease progresses on a CDK4/6 inhibitor.