• Female patients aged ≥18 and ≤75 years with histologically confirmed breast cancer.

• ECOG performance status of 0 to 2.

• HER2-positive or HER2-low invasive breast cancer, defined as:

• HER2-positive: IHC 3+ or IHC 2+ with FISH amplification; HER2-low: IHC 2+ without FISH amplification, or IHC 1+.

• Confirmed diagnosis of breast cancer brain metastases.

• Patients may have received prior chemotherapy (from first-line to multiple lines), HER2-targeted therapy (monoclonal antibodies), endocrine therapy, and immunotherapy.

• Adequate organ function as defined below:

• Hematology:

• Absolute neutrophil count (ANC) ≥ 1.5 × 10⁹/L; Platelet count (PLT) ≥ 80 × 10⁹/L (no blood transfusion within 14 days prior to first dose); Hemoglobin (Hb) ≥ 80 g/L;

• Serum biochemistry:

• Total bilirubin (TBIL) ≤ 1.5 × upper limit of normal (ULN); ALT and AST ≤ 2.5 × ULN; Blood urea nitrogen (BUN) and serum creatinine ≤ 1.5 × ULN;

• Cardiac function:

• Echocardiography: Left ventricular ejection fraction (LVEF) ≥ 45%.

• Subjects must voluntarily participate in the study and provide signed informed consent.