Malignant myoepithelioma of the parotid gland.

Myoepithelial cells are a significant component of most types of salivary gland neoplasms. A small but increasing number of case reports have also shown that pure myoepitheliomas form a distinct class of neoplasms with unique histological features. Previously reported cases have been either benign or, at most, locally aggressive. We present here a case of a malignant myoepithelioma of the parotid gland, confirmed by electron microscopy, that was locally aggressive and eventually metastasized. Review of this case and of existing reports indicates that myoepitheliomas exhibit a wide range of biological behavior that seems to correlate with their histological appearance.