Malignant glomus tumor of the leg developed in the context of a superficial typical glomus tumor

A 41-year-old man presented with a 2-cm painful subcutaneous nodule in his right leg, which had been present for more than 10 years and was recently enlarging. Histologically, the tumor was composed of sheets and nests of cells with variable cytomorphology, including typical round/ovoid glomus cells with clear cytoplasm and well-defined borders, small cells, and spindle cells. Numerous medium to large vessels were present. Nodules with moderate to high cellularity, nuclear atypia, and frequent mitotic figures (42 per 50 high-power fields) were noted. Immunohistochemistry showed cytoplasmic and membranous expression of smooth-muscle actin, vimentin, and membranous expression of type IV collagen. Whereas superficiality, dimensions, and long-term follow-up may suggest classification as a symplastic or uncertain potential glomus tumor (GT), histological features and immunoprofile are indicative of malignant nodules developed in a typical GT. The follow-up has been negative for recurrence/metastases. A search of the literature revealed 17 cases of malignant GTs between 1995 and 2010, all fatal, of which 10 had skin as the primary site.