[Secondary high-malignant transformation of a low-malignant epithelial-myoepithelial carcinoma].

The rare entity of epithelial-myoepithelial carcinoma (EMC) belongs to a group of tumors with a biphasic ductular growth pattern, mostly with a dominating myoepithelial component and low-grade malignancy. We report on the rare constellation of a primary low-malignant EMC with high malignant transformation (so-called dedifferentiation) into a highly malignant myoepithelial carcinoma. In the eight published cases so far, the high-malignant component was reported to be either adenocarcinoma or undifferentiated carcinoma or was otherwise not specified. To the best of our knowledge, this is the first case report of a high-grade myoepithelial carcinoma transforming from a low-grade EMC. We discuss interesting parallels to the pathogenesis of secondary transformation of carcinoma ex pleomorphic adenoma.