Targeted therapy with trastuzumab for epidermal growth factor receptor 2 (HER2)-positive advanced salivary duct carcinoma: A case report

Herein we report two cases of advanced and/or metastatic salivary duct carcinoma that relapsed after standard first-line chemotherapy. As overexpression of human epidermal growth factor receptor 2 (HER2) (3+) was observed by immunohistochemistry, the patients were treated with trastuzumab plus paclitaxel. One patient showed a complete response lasting over 2.5 years after the commencement of therapy; however, the other patient had no response to trastuzumab combined therapy. Dual fluorescence in situ hybridization was performed after the initiation of chemotherapy; the first case was positive for HER2 gene amplification, while the second case was negative. Our experiences suggest that therapy with HER2 blockers should be considered as options for treatment of HER2-positive salivary duct carcinoma. However, HER2 protein overexpression and gene amplification should be investigated further as therapeutic biomarkers.