Different treatment regimens following progression on CDK4/6 inhibitors.

Exploring the Efficacy and Safety of Different Systemic Treatment Regimens after CDK4/6i Progression in the Real World has significant implications. This study is an observational, real-world study. It plans to include over 300 eligible HR+/HER2- metastatic breast cancer patients who are currently receiving or planning to receive endocrine therapy regimens containing CDK4/6 inhibitors. This study is a single-arm, non-interventional study that evaluates the efficacy and safety of the first-line treatment regimen, which includes CDK4/6 inhibitors combined with endocrine therapy, based on clinical guideline consensus. After disease progression on first-line treatment, the second-line systemic treatment regimen (including but not limited to switching to another CDK4/6 inhibitor combined with endocrine therapy, other types of endocrine therapy, chemotherapy, targeted therapy, etc.) will be chosen by the physician, and the efficacy and safety of subsequent treatment will be evaluated. Additionally, peripheral blood ctDNA testing will be used to assess changes in baseline and progression-related biomarkers, including ESR1, PI3KCA, FGFR1, PTEN, among some patients.