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

"Radiation therapy SRT will be implemented according to investigator's clinical practice(based on brain metastases number and tumor volume). T-DXd(5.4mg/kg, once per 21 days, initiated within 2 weeks after SRT) will be provided to patients with confirmed HER2 positive breast cancer and brain metastasis until tumor progression, a severe adverse event deemed related to the study drug, or death. All dose adjustments should be based on the most severe toxicity level (CTCAE version 5.0) that occurred. Two doses are allowed to be reduced.~Dose Level 0: 5.4mg/kg Dose Level 1 :4.4mg/kg Dose Level 2: 3.2mg/kg"