Myoepithelial carcinoma (malignant myoepithelioma) is a rare salivary gland tumor composed entirely of myoepithelial cells that exhibit a dual epithelial and smooth muscle phenotype. The tumor shows wide morphologic and cytologic diversity in a similar way to its benign counterpart, myoepithelioma, with evidence of malignant change. The malignancy manifests mainly as an infiltrative growth pattern, angiolymphatic and/or perineural invasion, with a propensity for mostly distant metastasis and occasional regional lymph node involvement. Other corroborative evidence of malignancy such as necrosis and increased mitotic activity can also be seen.
Originally described by Stromeyer et al in 1975,
Barnes et al renewed interest in this rare entity in 1985 after describing 3 cases of myoepithelial carcinoma (malignant myoepithelioma) in their review of myoepitheliomas of the head and neck.
However, it was Dardick et al’s detailed descriptions of myoepitheliomas that were crucial in furthering the understanding of myoepithelial tumors.
Their articles helped to increase the accuracy of describing ensuing reported cases of myoepithelial carcinoma (malignant myoepithelioma). In 1991, myoepithelial carcinoma was added to the second edition of the World Health Organization (WHO) classifications of malignant salivary gland tumors.
Many of these tumors arise as a malignant transformation in the setting of a benign pleomorphic adenoma or a benign myoepithelioma,
and myoepithelial carcinoma (malignant myoepithelioma) is particularly seen in association with recurrence of these benign tumors.
Other such tumors arise de novo.