Malignant Myoepithelioma of the Parotid Gland: Cytologic and HistologicFeatures

Overview

A case of malignant myoepithelioma of the parotid gland in a 34-year-old female is presented. Inthe fine-needle aspiration material, there was predominance of poorly cohesive polygonal cellswith marked nuclear pleomorphism; no mitotic figures were observed. Focally, fragments ofmyxoid metachromatic intercellular material were also present.Histologically, the tumor was encepsulated, showing focal invasion of the capsule and tumorthrombi in the capsular vessels. The tumor was predominantly solid and myxoid, composed ofcells with epithelioid features, marked anisonucleosis and a low mitotic activity.Immunohistochemically, the cells revealed positive staining for S-100 protein, vimentin, cytokera-tins, glial acidic fibrillary protein and carcinoembryonic antigen; only several cell groups expres-sed smoth muscle actin and desmin; muscle specific actin was uniformly negative.In differential diagnosis, it was important to distinguish malignant myoepitelioma mainly frompleomorphic adenoma (mixed tumor), benign myoepithelioma, carcinoma ex pleomorphic adeno-ma and malignant melanoma. The criteria of malignancy in myoepithelial tumors are discussed.

Key words:
salivary gland - myoepithelial tumors - malignant myoepithelioma - fine-needle aspira-tion cytology - immunohistochemistry