Complete Response to Trastuzumab-Based Chemotherapy in a Patient with Human Epidermal Growth Factor Receptor-2-Positive Metastatic Salivary Duct Carcinoma ex Pleomorphic Adenoma

INTRODUCTION Carcinoma ex pleomorphic adenoma (CXPA) of the salivary glands has often a salivary duct carcinoma (SDC) component, which resembles ductal carcinoma of the breast and frequently overexpresses human epidermal growth factor receptor-2 (HER2). We report a case of metastatic CXPA with SDC component who was treated with trastuzumab-based chemotherapy and has had a durable complete response. CASE REPORT A 74-year-old man was diagnosed with CXPA of the right parotid gland. The resected tumor was histologically diagnosed as CXPA with a predominant SDC component that showed strong positivity for HER2 protein and HER2 gene amplification. Multiple pulmonary metastatic lesions were detected after surgery, and combination chemotherapy with paclitaxel and trastuzumab was initiated. A complete response was confirmed after 7 treatment cycles, and no evidence of disease progression has been observed after 13 months of initiation of therapy. CONCLUSIONS This report suggests a potential utility of trastuzumab-based chemotherapy for HER2-positive CXPA.