Dedifferentiated epithelial-myoepithelial carcinoma of the parotid gland with aberrant expression of prostate specific antigen: a case report.

This report describes a rare case of dedifferentiated epithelial-myoepithelial carcinoma (EMCa) of the parotid gland. The tumor had 2 distinct components; a well-differentiated EMCa comprising of ductal and myoepithelial cells with low nuclear grade and low proliferation index. The second component showed a completely different morphology comprising of sheets and clusters of poorly differentiated cells with high nuclear grade and proliferative activity. The dedifferentiation was associated with an accelerated clinical course. Dedifferentiated EMCa is extremely rare with only 8 cases reported in the English literature. An unusual feature, hitherto not described in this tumor is the aberrant expression of prostate-specific antigen in the dedifferentiated component. In male patients, this may cause diagnostic confusion with metastatic prostate carcinoma.