A Phase II Study of T-DXd Plus SRT in HER2-positive Breast Cancer Brain Metastases

Inclusion Criteria: Pathologically confirmed HER2 positive advanced breast cancer Age>18 years. Brain metastases confirmed by enhanced brain MRI. Metastases number less than 15. KPS≥70 or KPS ≥60 with neurologic symptoms caused by BM Life expectancy of more than 6 months Prior therapy of oral dexamethasone not exceeding 16mg/d Time interval from prior therapy was more than 2 weeks, and evaluation of adverse events is no more than grade 1. 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 Signed the informed consent form prior to patient entry Exclusion Criteria: Leptomeningeal or hemorrhagic metastases 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