CDK4/6 inhibition in early and metastatic breast cancer: A review

Breast cancer (BC) is responsible for 14% of cancer-related deaths in women [1]. Cyclin-dependent kinase (CDK) 4/6 inhibitors are a new class of selective drugs, offering an effective and tolerable treatment. CDK4/6 inhibitors induce cell cycle arrest in the G1 phase, and may thereby prevent tumour progression. Three CDK4/6 inhibitors have been tested in clinical BC trials: palbociclib, ribociclib, and abemaciclib. The Food and Drug Administration (FDA) and European Commission (EMA) have approved palbociclib for the treatment of patients HR+ HER2- locally advanced or metastatic BC (aBC) in combination with an aromatase inhibitor as initial therapy in postmenopausal women or in combination with fulvestrant in women who have received prior endocrine therapy. Ribociclib has been approved by the FDA in combination with an aromatase inhibitor as initial therapy for postmenopausal women with HR+ HER2- aBC. Moreover, CDK4/6 inhibitors have shown promising results in the (neo)adjuvant setting. In this review, the principal completed and ongoing clinical trials in aBC are reviewed for both the metastatic as (neo)adjuvant setting. Tables will provide a complete overview of the ongoing clinical trials. At last, the future perspectives of these CDK4/6 inhibitors are discussed.