Low-grade salivary duct carcinoma: description of 16 cases.

Low-grade salivary duct carcinoma is a rare neoplasm. We report on 16 patients, with a median age of 64 years. All but one tumor arose from the parotid gland, including one tumor that arose in an intraparotid lymph node; one arose in the submandibular gland. Tumors consist of single to multiple dominant cysts, accompanied by adjacent intraductal proliferation. Cysts are lined by small, multilayered, proliferating, bland ductal cells with finely dispersed chromatin and small nucleoli. Separate, smaller ductal structures are variably filled by proliferating ductal epithelium with cribriform, micropapillary, and solid areas. The overall appearance is very similar to breast atypical ductal hyperplasia and low-grade ductal carcinoma in situ. Foci of definitive stromal invasion were seen in four tumors. Two tumors demonstrated transition from low- to intermediate- or high-grade cytology, with scattered mitotic figures and focal necrosis. S-100 revealed diffuse strong expression in all 9 cases studied. Myoepithelial markers (calponin) highlighted supportive myoepithelial cells rimming the cystic spaces, confirming the intraductal nature of most, or all, of six tumors studied. Nine tumors studied for Her2-neu antigen were uniformly negative. Follow-up was obtained on 13 of our 16 patients. All patients were disease-free after surgery 6 to 132 months (median 30 months). Low-grade salivary duct carcinoma is a low-grade neoplasm with an excellent prognosis; it may be treated by conservative but complete resection. Its resemblance to atypical breast ductal hyperplasia, or micropapillary/cribriform intraductal carcinoma, distinguishes it from high-grade salivary duct carcinoma, papillocystic acinic cell carcinoma, and cystadenocarcinoma.