Multicenter retrospective study of survival following progression of HR-positive HER2-negative metastatic breast cancer on ET plus CDK4/6 inhibition

Endocrine therapy (ET) plus CDK4/6-inhibitor is the standard first-line treatment for patients with HR-positive, HER2-negative metastatic breast cancer (HR+ HER2- mBC). The optimal therapy after progression on this therapy is not clear. A multicenter retrospective cohort study in Italy included 506 patients with HR+ HER2- mBC that progressed during ET plus CDK4/6 inhibitor therapy, who received ET-based or chemotherapy (CT)-based treatments. Younger age, de novo metastatic disease, and visceral involvemen were independent factors associated with shorter progression-free survival. Additionally, a duration of prior CDK4/6 inhibitor therapy exceeding 12 months was associated with significantly longer overall survival. The authors conclude that duration of prior CDK4/6 inhibitor therapy and presence of visceral involvement were key factors that affect treatment decision.