Myoepithelial carcinoma of the parotid gland.

Rare malignant tumor of the salivary gland, a myoepithelial carcinoma, arose de novo in the right parotid gland. The initial tumor was composed predominantly of myoepithelial cells. Subsequently the tumor recurred three times, with infiltration of the bones of the cranial base. Histological examination showed sarcomatoid neoplasm composed of malignant spindle cells with high mitotic rate and perineural invasion. There was no involvement of cervical lymph nodes. Immunohistochemistry demonstrated myoepithelial differentiation: tumor cells were positively stained with vimentin, alpha smooth muscle actin and S-100 protein antibodies, and focal positively was noticed with cytokeratin (AE1/AE3) antibody. Large number of tumor cells nuclei was reactive with the monoclonal anti-p63 antibody, clone 4A4. Myoepithelial carcinomas exhibit a wide spectrum of morphological heterogeneity and for that reason could be confused with many tumors. Cytoarchitectural patterns and immunohistochemical profile are crucial for identification. These tumors are malignant neoplasms with diverse clinical outcomes, sometimes very aggressive.