Background: Salivary duct carcinoma (SDC) is a distinctive salivary gland neoplasm morphologically characterized by intraductal and infiltrating components. Most tumors occur in the major salivary glands and demonstrate a propensity for invasive growth with early regional and distant metastases. Therefore, SDC is regarded as a high-grade malignancy in the current classification of salivary gland neoplasms.
Methods: In an effort to identify clinically relevant prognostic features, we studied the clinicopathologic and immunohistochemical findings in 15 SDC, with ultrastructural evaluation of three tumors.
Results: Thirteen SDC occurred in the parotid gland, one in the Stensens duct, and one in the palate. Twelve patients were men (ratio of men to women = 4:1). Patients ranged in age from 39 to 81 years (mean = 59 years). Tumor size varied from 1.2 to 6.5 cm (mean = 3.1 cm). An intraductal component was identified in 10 of 14 primary SDC that made up 10% to 95% of the tumor. In three SDC a preexisting pleomorphic adenoma was identified. Immunohistochemical and electron microscopic evaluation showed the SDC to be composed entirely of ductal cells, and one tumor exhibited features of striated duct differentiation.
Conclusions: SDC show a broader clinicopathologic spectrum than previously described. The tumor may arise in a pleomorphic adenoma. The proportion of intraductal and extraductal growth is variable and of prognostic significance. Although the majority of SDC behave in a high-grade fashion, those with a predominant intraductal component of greater than 90% (PID-SDC) and minimally invasive (< 8 mm) SDC in pleomorphic adenoma appear to have a more favorable prognosis.