[Three Cases of HER2-Positive Breast Cancer Brain Metastases That Responded to T-DXd after Whole-Brain Radiation Therapy and Subsequent Tumor Regrowth].

Case 1: A 49-year-old woman underwent NAC followed by surgery for left breast cancer. Two years later, she experienced recurrence with lymph node and liver metastases. Nine months after, multiple brain metastases appeared, which shrank after whole-brain radiation therapy. One year post-radiation, the tumors regrew, and T-DXd was administered, leading to a positive response. However, 22 months later, the disease progressed, and she died from carcinomatous meningitis 26.6 months after treatment. Case 2: A 48-year-old woman had NAC followed by surgery for right breast cancer. One year and 9 months post-surgery, she had a brain metastasis recurrence, treated with resection and Gamma Knife. Six months later, the tumors regrew and were resected again. One year after, multiple brain metastases appeared, treated with whole-brain radiation therapy. Initially, the tumors shrank but regrew, so T-DXd was administered, achieving a complete response. However, 19.1 months later, the disease progressed with lung metastases, and she died from carcinomatous meningitis 21.9 months post-treatment. Case 3: A 47-year-old woman with Stage Ⅳ left breast cancer(lung, liver, and bone metastases)continued chemotherapy. After multiple brain metastases appeared, whole-brain radiation therapy and T-DM1 led to tumor shrinkage. However, the tumors rapidly regrew, and T-DXd was started, resulting in a positive response. Ten months later, the disease progressed, and she died from carcinomatous meningitis 17.7 months after initial treatment.