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):

  1. Absolute Neutrophil Count (ANC) ≥ 1.5 x 109/L, Platelets≥ 90 x 109/L, Hemoglobin ≥ 90 g/L
  2. Aspartate aminotransferase/alanine aminotransferase (AST/ALT) ≤2.5 x ULN without liver metastasis,≤ 5 x ULN with liver metastases
  3. Serum BUN and creatinine ≤ 1.5 x Upper Limit of Normal (ULN)
  4. LVEF ≥ 50%
  5. QTcF \< 480 ms
  6. 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