Hybrid Tumor of the Parotid Gland: A Case Report and Review of the Literature

Figure 2

(a) Epithelial-myoepithelial carcinoma. The ductal structures are composed of outer layer of polygonal, clear myoepithelial cells with variable sized and shaped nuclei. The central epithelial cells are smaller and have eosinophilic cytoplasm, round to oval nuclei, and a high nuclear to cytoplasmic ratio. (b) Focally, the epithelial-myoepithelial carcinoma component exhibits myxochondroid rich background with anastomosing stands of epithelial cells reminiscent of pleomorphic adenoma morphologically. (c) Basal cell adenocarcinoma: prominent eosinophilic hyaline material is seen around nodules of tumor composed of small cells with more chromatic nuclei around larger cells with paler nuclei. (d) Adenoid cystic carcinoma: tubular and cribriform and solid tumor nests. Basal lamina-containing cyst-like spaces are noted. The tumor cells show high grade cytology with markedly increased nuclear to cytoplasmic ratio. (e) Nests of tumor invading the peripheral portion of the nerve bundle in the areas dominated by adenoid cystic carcinoma. (f) The proliferative index by Ki-67 stain labeling showed significantly higher labeling index in the adenoid cystic component (lower left corner) in comparison to the epithelial-myoepithelial component (upper right corner).