Low-grade salivary duct carcinoma of the parotid gland: report of a case with immunohistochemical analysis.

Salivary duct carcinoma (SDC) is a highly aggressive malignancy of the salivary glands. However, one type of SDC, which shows minimal invasion and better prognosis, is known as low-grade SDC (LG-SDC). This report presents an additional case of LG-SDC of the parotid gland. The patient was a 38-year-old Japanese woman who noticed painless swelling of the left parotid region. Grossly, the cut surface of the tumor was cystic. Microscopically, the tumor showed a multicystic pattern, which was lined by eosinophilic to clear atypical cells with cribriform or Roman bridge patterns. An immunohistochemical examination revealed the tumor was positive for cytokeratin (CK) 7 and epithelial membrane antigen, partially positive for androgen receptor and gross cystic disease fluid protein-15, and diffusely positive for Her-2/Neu, progesterone, and estrogen receptors. The cancer cells showed focal immunopositivity for S-100 protein. Immunostaining for p63, CK14, and calponin showed an in situ pattern in most areas of this tumor, whereas the tumor showed minimal invasion. The cancer cells were diffusely positive for MUC1 and MUC6 and focally positive for MUC2 and MUC4. Finally, the tumor was diagnosed to be LG-SDC. The differential diagnosis and the mucin pattern were evaluated.