A 52-year-old female with stage Ⅳ, bilateral, HER2-positive, breast cancer as well as bilateral axillary lymph node(LN) metastasis and bilateral pulmonary metastasis was administered trastuzumab plus pertuzumab plus docetaxel as a standard chemotherapy. After this treatment the right breast cancer, right axillary LN metastasis, and bilateral pulmonary metastases contracted, while the left breast cancer and left axillary LN metastasis expanded. Trastuzumab emtansine was then administered, and the left axillary LN metastasis contracted, however, the left breast cancer expanded, resulting in marked breast engorgement. When trastuzumab deruxtecan(T-DXd)was administered, the left breast cancer contracted for the first time during the overall treatment process, and the signs of breast inflammation disappeared. Other lesions showed no recrudescence. T-DXd was administered seven times, and, at the stage of maximum contraction during the treatment period, a total left mastectomy and left axillary LN dissection were performed. Pathological examination then confirmed that tumor cells were no longer present in the left breast and left axillary LN. In this case T-DXd was highly effective for the local treatment of intractable, HER2-positive, breast cancer.