Endocrine therapy combined with targeted therapy in hormone receptor-positive metastatic breast cancer

Increasing numbers of targeted drugs are used in hormone receptor (HR)-positive metastatic breast cancer (MBC) to overcome or delay resistance to endocrine therapy. This study will systemically review the progress made in endocrine therapy combined with targeted therapy in the treatment of HR-positive MBC. From the "AI (aromatase inhibitor) era" represented by aromatase inhibitors, we have gradually entered the "post-AI era" represented by fulvestrant. Under the guidance of research on the molecular mechanism of endocrine therapy resistance, the "combination of endocrine therapy and targeted therapy" era is approaching. The development of drugs that target endocrine therapy resistance has concentrated on cyclin-dependent kinase 4/6 inhibitors, histone deacetylase inhibitors, and inhibitors of drug targets in the phosphatidylinositol 3 kinase-protein kinase B-mammalian target of rapamycin (PI3K-AKT-mTOR) pathway, providing new strategies for HR-positive MBC. Exploring biomarkers to guide the more precise use of targeted drugs in endocrine therapy for MBC is the focus of current and future research.