Abemaciclib in HR+/Her2-metastatic breast cancer patients after previous progression on palbociclib or ribociclib: Clinical experience in a tertiary hospital in Madrid, Spain

Preclinical and pharmacological data of the three approved cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) suggest differences among them. Abemaciclib inhibits other targets (CDK2/Cyclin A/E and CDK1/Cyclin B) causing cell cycle arrest in phases G1 and G2. In preclinical models, both senescence and apoptosis occurred earlier and at lower concentrations of Abemaciclib, compared to treatment with either palbociclib or ribociclib. Abemaciclib monotherapy or combined with tamoxifen has demonstrated activity in endocrine refractory metastatic breast cancer (MBC) who had received prior treatment with chemotherapy.