Malignant glomus tumor: a rare case with an ultrastructural study

Glomangiosarcoma is an extremely rare neoplasm that represents 1% of all glomus tumors, which in turn make up 2% of soft tissue tumors. We discuss the case of a 49-year-old woman who had a slow growing tumor on the left foot dorsum which evolved over a 4-year period. Magnetic resonance imaging (MRI) was performed showing deep, partially infiltrative, heterogeneous soft tissue mass with necrosis. Tru-Cut biopsy was done with a malignant glomus tumor report. Treatment consisted of wide resection and intense rehabilitation program resulting in full-function recovery. The definitive diagnosis based on morphologic, immunohistochemical and ultrastructural studies evidenced a conventional glomus tumor with malignant areas and abrupt transition to dedifferentiated component with myxoinflammatory fibroblastic sarcoma (MIFS) features. To the best of our knowledge, this is the first case showing this kind of dedifferentiation, the ultrastructural characteristics in this study allow us to identify a very rare disease and unique differentiation.