A case of HER-2-positive recurrent breast cancer showing a clinically complete response to trastuzumab-containing chemotherapy after primary treatment of triple-negative breast cancer

We report a case of HER-2-positive recurrent breast cancer showing a clinically complete response to trastuzumab-containing chemotherapy 6 years after primary treatment of triple-negative breast cancer. The primary tumor was negative for HER-2 as determined by immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) (1+, and ratio, 1.1), but examination of the recurrent lymph node metastasis showed positivity for HER-2 by FISH (ratio, 5.2). No lesions were detected in either her left breast or in other organs, and the patient was diagnosed as having HER-2-positive recurrent disease. Combination chemotherapy using weekly paclitaxel and trastuzumab was initiated, and a clinically complete response was achieved. This report suggests the benefit of routine evaluation of HER-2 status in recurrent breast cancer with the introduction of HER-2-targeting agents.