Histological and immunohistochemical features of a recurrent epithelial-myoepithelial lacrimal gland tumor in a dog

Purpose: To describe histological and immunohistochemical features of a rare lacrimal gland tumor. Methods: A conjunctival mass in the upper eyelid, lateral cantus, was surgically excised from an 11 year-old female mongrel dog. Eight months later the dog presented with recurrence of a larger orbital mass, and complete orbital exenteration was performed. Samples from both surgeries were formalin fixed and submitted for histology. Microtomic sections were stained with hematoxylin and eosin and serial sections immunostained with the standard ABC method in order to characterize neoplastic cells. Monoclonal antibodies antivimentin, cytokeratin 14 (CK14), CK19, CK8/18 and alpha smooth-muscle-actin (aSMA) were applied. AEC served as the chromogen. Results: Histologically, the first mass excised was a large, capsulated, neoplastic nodule with expansive growth. The second mass was a large multilobulated un-encaspulated nodule with multifocal signs of infiltrative growth. In both tumors two distinct cell populations were present: cuboidal cell lining small ductular structure and elongated cells with scant, clear cytoplasm disposed in short bundles or in whorls around ductal structures. Cuboidal cells were positive for CK19 and CK8/18, spindle cells were CK14 and aSMA positive. Both cell types were vimentin negative. Based on histological and immunohistochemical feature a diagnosis of epithelial-myoepithelial carcinoma (ECM) was posed. Conclusions: ECM is a rare tumor of lacrimal gland, whose histological features parallel those of salivary tumors, in which both component of secretory parenchyma, i.e. epithelial and myoepithelial cells, undergo neoplastic transformation. Further investigations are necessary to understand the specific prognostication criteria for this type of neoplasm.