A case with HER2-overexpressing breast cancer completely responded to humanized anti-HER2 monoclonal antibody.

This is a case report of a 57-year-old woman with a history of primary carcinoma of the right breast with metastases to the contralateral axillary lymph node. After a partial response (PR) was induced by high-dose chemotherapy with peripheral blood stem cell transplantation, she underwent mastectomy with biopsy of the bilateral axillary lymph nodes. Six months after surgery, the patient had multiple lung metastases. She was then treated with five cycles of fluorouracil, mitoxantrone and vindesine. Although a PR was achieved, further chemotherapy could not be given because of cardiac dysfunction. Since immunohistochemical staining for the HER2 gene product was strongly positive on the surface of primary tumor cells, humanized anti-HER2 monoclonal antibody (trastuzumab) was given intravenously. The metastatic lesion decreased in size and finally appeared to be only cicatricial. Twenty-one months after the initial administration of trastuzumab, the pulmonary lesion was excised. The pathological examination revealed no tumor cells in the resected specimen so further treatment was stopped. The relapse-free state has continued for 24 months after the pulmonary resection.