Coexistence of salivary duct, myoepithelial and epithelial-myoepithelial carcinomas in the parotid gland: a case report and literature review.

Few reports have described two or more histologically-distinct carcinoma types within the same salivary gland. A 62-year-old man presented to our hospital after detecting a mass in the right parotid gland. Computed tomography revealed a tumor (5.1 × 5.0 cm) within the right parotid gland. Tumor resection with lymph node dissection was performed. The proliferation of three morphologically-different tumor cells was demonstrated on histopathologic examination (salivary duct carcinoma [SDC], myoepithelial carcinoma and epithelial-myoepithelial carcinoma [EMC]). The shape of the inner layer of cells in the EMC was similar to the SDC. Specifically, it appeared that the cells were a mixture of the two tumors with reciprocal transfer in the same area. Immunohistochemical staining showed that the SDC cells and the EMC inner cells were positive for AR, HER2 and p53. Thus, we suggest that our case represented a high-grade transformation.