Hybrid Carcinomas of Salivary Glands

To the Editor.—We read with interest the article by Croitoru and colleagues1 on hybrid carcinomas of salivary glands. Interestingly, we encountered a hybrid tumor of the parotid gland in a 58-year-old man. A partial parotidectomy was performed, and the gross specimen consisted of a firm pale tumor measuring 2.5 cm in maximal dimension. Microscopic examination showed that the single tumor mass observed on gross inspection was composed of 2 tumors: epithelial-myoepithelial and mucoepidermoid carcinomas. The former was typical with a biphasic pattern of central epithelial lined ductular structures cuffed by proliferating clear myoepithelial cells. Hyalinized basement membrane–like material and fibrous tissue bands separated this neoplasm into lobules. The mucoepidermoid carcinoma was composed mainly of squamoid cells, together with distinct mucous-containing cells and so-called intermediate cells. Adjacent to the tumor, within the surrounding non–tumorous parotid parenchyma, proliferating intercalated ducts were observed. These blended with the epithelial-myoepithelial carcinoma and were at the periphery of the muco-epidermoid component. Parenchyma more distant from the tumor appeared normal. This tumor qualifies as a hybrid neoplasm because there were 2 distinct tumors in the same topographic area producing a single clinical and macroscopic tumor mass.Whilst we agree that adequate tissue sampling and accurate identification of components is important in determining biologic behavior and thus appropriate treatment, interesting pathogenetic questions are raised.In 2 of the cases in the article by Croitoru et al, in 3 of the 6 cases described in the literature review, and in the case that we describe, one of the components was an epithelial-myoepithelial carcinoma. It has been stated of epithelial-myoepithelial carcinomas “that apparent collision tumors, though uncommon, seem to arise more frequently than would be expected purely by chance.”2Furthermore, Di Palma3 also noted the coexistence of intercalated duct hyperplasia with epithelial-myoepithelial carcinoma. It was suggested that multidirectional differentiation may be mediated with intercalated duct hyperplasia and may account for the simultaneous occurrence of more than 1 tumor, especially in association with epithelial-myoepithelial carcinoma.We believe an additional important diagnostic message is that when one encounters an epithelial-myoepithelial carcinoma (especially in salivary glands), then one should actively look for other accompanying tumors, which may be more aggressive and thus guide management strategies.