A Phase II Study of SHR-A1811 Combined With Radiotherapy in HER2-positive and HER2-low Breast Cancer Brain Metastases

Inclusion criteria

• Pathologically confirmed HER2 positive (IHC 3+ or IHC 2+/FISH+)or HER2-low(IHC1+ or 2+/FISH-) advanced breast cancer
• Age>18 years.
• newly diagnosed Brain metastases confirmed by enhanced brain MRI. Metastases number less than 6.
• No more than four lines of previous advanced therapy
• Life expectancy of more than 3 months
• There were no known or suspected leptomeningeal brain metastases
• The interval from previous therapy was more than 2 weeks, and acute toxicity from previous therapy had to resolve to grade 1 or less
• The use of mannitol, bevacizumab, or hormone therapy was allowed before enrollment, but the dose was stable for at least a week without the need for an increment
• Screening laboratory values must meet the following criteria( and should be obtained within 28 days prior to registration):

Absolute Neutrophil Count (ANC) ≥ 1.5 x 109/L, Platelets≥ 90 x 109/L, Hemoglobin ≥ 90 g/L Aspartate aminotransferase/alanine aminotransferase (AST/ALT) ≤2.5 x ULN without liver metastasis,≤ 5 x ULN with liver metastases Serum BUN and creatinine ≤ 1.5 x Upper Limit of Normal (ULN) LVEF ≥ 50% QTcF < 480 ms INR≤1.5×ULN，APTT≤1.5×ULN 10.Signed the informed consent form prior to patient entry

Exclusion criteria

• Leptomeningeal or hemorrhagic metastases
• previously used T-dxd
• Uncontrolled epilepsy
• Severe or uncontrolled disease: severe cardiovascular disease, end-stage renal disease, severe hepatic disease, history of immunodeficiency, including HIV positive, active HBV/HCV or other acquired congenital immunodeficiency disease, or organ transplantation history, active infection, etc.
• History of allergy to treatment regimens
• Pregnancy or lactation period， women of child-bearing age who are unwilling to accept contraceptive measures.
• Inability to complete enhanced MRI
• Not suitable for inclusion for specific reasons judged by sponsor -