Cyclin-dependent kinases 4 and 6 (CDK4/6) inhibitors combined with hormonal therapy are the current standard frontline treatment for patients with hormone receptor-positive (HR+), human epidermal growth factor receptor 2 (HER-2)-negative metastatic breast cancer (MBC). However, the optimal treatment after progression on CDK4/6 inhibitors remains unknown. Anlotinib is an oral multi-target tyrosine kinase inhibitor (TKI) that strongly inhibits VEGFR, PDGFR, FGFR, and c-kit. This study aimed to evaluate the safety and efficacy of anlotinib-based combination therapy in patients with HR+ MBC previously treated with a CDK4/6 inhibitor.

Inclusion Criteria:

• Female patients aged 18 to 75 years, with an ECOG score of 0-1, and an expected survival of at least 3 months;
• Presence of measurable lesions as defined by RECIST 1.1 criteria;
• Histopathologically confirmed HR-positive/HER2-negative breast cancer. HER2 negativity is determined by an immunohistochemistry (IHC) result of HER2 (0/1+). If the result is HER2 (++), a FISH or CISH test is required to confirm the absence of HER2 amplification;
• Patients who have undergone multiple lines of advanced therapy with no remaining standard treatment options;
• Prior treatment with at least one line of CDK4/6 inhibitors and endocrine therapy;
• Disease progression following aromatase inhibitor (AI) or fulvestrant combined with CDK4/6 inhibitors, either as adjuvant therapy or as systemic treatment for advanced disease.

Exclusion Criteria:

• Patients with HER2-positive breast cancer confirmed by histology or cytology;
• Patients who discontinued therapy due to non-disease progression reasons, such as adverse events or other non-medical factors;
• Detection of a second primary malignant tumor at the time of enrollment;
• Failure to complete CDK4/6 inhibitor therapy;
• Pregnant or breastfeeding patients;
• Presence of third-space fluid accumulation (e.g., pleural effusion, ascites, pericardial effusion) that cannot be managed through drainage or other methods;
• Patients previously treated with anti-angiogenic agents, including small molecules such as anlotinib or apatinib, and large molecules such as bevacizumab;
• Patients currently receiving any other anti-tumor treatment for any other malignancies.

HR+ metastatic breast cancer previously treated with CDK4/6is