This multicenter, prospective observational cohort study aims to investigate the impact of circulating tumor DNA (ctDNA) level and key actionable gene mutation status on prognosis and treatment response in patients with advanced hormone receptor-positive / human epidermal growth factor receptor 2-negative (HR+/HER2-) breast cancer.

This is a non-interventional, real-world observational study. Patients with histologically confirmed advanced HR+/HER2- breast cancer, aged ≥18 years, with expected survival >3 months, who consent to ctDNA testing will be enrolled. A total of 400 patients will be recruited from multiple centers in China. Peripheral blood (10 mL) will be collected for ctDNA next-generation sequencing panel testing. Results will be returned to clinicians, who decide on subsequent treatment independently. Baseline data, treatment history, treatment regimens, and efficacy assessments (imaging every 8-12 weeks) will be recorded. Follow-up will continue until death or study end. Primary endpoint: overall survival (OS). Secondary endpoints: progression-free survival (PFS), objective response rate (ORR), correlation of ctDNA level/mutations/clonality with treatment response and OS, and correlation of testing timing/clinical decisions with OS. Statistical analysis will use intention-to-treat (ITT) principle, Kaplan-Meier, Cox regression, and subgroup analyses.

Inclusion Criteria:

• Histologically confirmed advanced breast cancer, molecular subtype HR+/HER2-
• Age ≥18 years
• Expected survival >3 months
• Willing to undergo ctDNA testing and sign informed consent form

Exclusion Criteria:

• The subject has not signed the informed consent form.
• Pregnant or breastfeeding women.
• Other situations deemed by the investigator as unsuitable for inclusion in the study.

Patients with histologically confirmed advanced HR+/HER2- breast cancer.