Malignant mixed tumor ex eccrine spiradenoma: an unusual pattern of malignant dedifferentiation

Eccrine spiradenoma (ES) is a benign tumor of the skin adnexal origin. It is often seen in the head and neck region of young adults and may be present for years. While there have been numerous case reports of malignant degeneration within ES, they have been mostly carcinomatous dedifferentiation and rarely carcinosarcomas. A malignant mixed tumor is a neoplasm with a malignant epithelial component and areas of chondroid and myxoid differentiation within the malignant epithelial proliferation. While the epithelial component is malignant, the mesenchymal component is felt to represent a benign, metaplastic response of the stroma. While the malignant mixed tumor has a benign counterpart, the benign mixed tumor, the former is usually not seen in continuity with the latter. We describe a case of ES with malignant degeneration and demonstrate the transformation from benign to malignant. The histology and immunohistochemistry of the neoplasm supports a malignant mixed tumor, an extremely unusual neoplasm to see in association with ES or any benign adnexal neoplasm.