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11 April 2012 - Case of the Week #238
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Thanks to Dr. Tihana Dzombeta, University of Zagreb, Croatia, for contributing this case. To contribute a Case of the Week, follow the guidelines on our Case of the Week page.
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Case of the Week #238
An 81 year old man had a painless tumor of his left great toe, which was excised. Macroscopically, the tumor was well-circumscribed, measured 4 x 3 x 2.5 cm and was located in the subcutis.
What is your diagnosis?
Symplastic glomus tumor
The tumor was encapsulated and composed of solid sheets of cells separated by vessels of varying size and lined with normal appearing, CD34+ endothelium. The neoplastic cells showed pronounced nuclear pleomorphism, hyperchromasia and occasional intranuclear inclusions. Mitotic activity was sparse, up to 2 mitoses/50 HPF, but the Ki-67 proliferative rate was about 25%. There were no atypical mitotic figures, but areas of necrosis were present. Tumor cells were diffusely immunoreactive for smooth muscle actin (SMA), vimentin and desmin.
Left to right: CD34, Ki-67
Left to right: smooth muscle actin, vimentin, desmin
Glomus tumors are neoplasms differentiating toward specialized cells found in the glomus body, a structure involved in thermoregulation (Arch Pathol Lab Med 2008;132:1448, Int J Surg Pathol 2011;19:499). Symplastic glomus tumors, first described in 1995 as epithelioid glomus tumors (Hum Pathol 1995;26:1022) have marked nuclear atypia but no other criteria for malignancy. Less than 25 cases have been reported in the English literature (Am J Dermatopathol 2009;31:71).
The differential diagnosis includes malignant glomus tumor, which has metastatic potential (AJ Cutan Pathol 2009;36:1099). A comprehensive study defined malignant glomus tumors as having a deep location and size >2 cm, or atypical mitotic figures, or moderate to high nuclear grade and 5 or more mitotic figures/50 HPF (Am J Surg Pathol 2001;25:1).
Symplastic glomus tumors have benign behavior, and excision is curative.
Nat Pernick, M.D., President
and Liz Parker, B.A., Associate Medical Editor
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Bingham Farms, Michigan (USA) 48025
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