[Stage Ⅳ HER2-Positive Breast Cancer That Showed Complete Response for Over One Year after Discontinuation of Anti-HER2 Therapy-A Case Report].

A 75-year-old woman with a left breast mass on breast cancer screening was referred to our hospital for detailed evaluation. Further examination revealed left breast cancer with metastases to the left axilla, left parasternal region, left supraclavicular fossa, mediastinum, and left hilar lymph nodes, as well as multiple lung metastases. Histopathological evaluation of a needle biopsy specimen revealed invasive ductal carcinoma(scirrhous type), and she was diagnosed with Stage Ⅳ human epidermal growth factor receptor 2(HER2)-positive breast cancer. Following diagnosis, treatment was initiated with trastuzumab, pertuzumab, and docetaxel; however, she developed hypersensitivity to docetaxel and received only trastuzumab and pertuzumab after the second course. We observed a complete response after 3 courses, and treatment was discontinued after 13 courses. She underwent regular evaluation after treatment discontinuation, and a complete response was maintained for 1 year and 6 months. We conclude that combination therapy comprising trastuzumab and pertuzumab was effective for Stage Ⅳ HER2-positive breast cancer and that a complete response could be maintained even after treatment discontinuation.