Malignant myoepithelioma arising from recurrent pleomorphic adenoma of minor salivary gland

Malignant myoepitheliomas of the salivary gland are very rare tumors which may either arise de novo or develop in a pre-existing pleomorphic adenoma. We report a case of malignant myoepithelioma of the minor salivary gland that progressed from benign pleomorphic adenoma. The original pleomorphic adenoma was resected in 1979 (the '79 tumor). The first recurrent tumor was operated in 1995 (the '95 tumor). The '95 tumor was diagnosed as pleomorphic adenoma. Although the myoepithelial tumor component was more prevalent in the '95 tumor, histological features of the first recurrent tumor were similar to the '79 tumor. The second recurrent tumor showed more aggressive clinical features (the '98 tumor). It also showed massive growth of myoepithelial tumor cells with bone invasion, which led to the diagnosis of the '98 tumor as malignant myoepithelioma. With adequate surgical margin, the patient has been free from tumor recurrence for 20 months.