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Case of the Week #289
Clinical History:
A 42 year old man presented with a painful nodular forearm mass.
Glomus tumors are immunoreactive for smooth muscle actin (as in this case), type 4 collagen and vimentin. There is variable expression of CD34, h-caldesmon and calponin, and no expression of keratin, desmin, S100 and chromogranin. CD31 highlights the vasculature, but tumor cells are CD31-.
Left: alpha-smooth muscle actin; right: CD31
The differential diagnosis of glomangioma includes capillary hemangioma, which lacks the alpha smooth muscle actin+ cells seen in this case. Eccrine spiradenoma is often painful, but is not arranged around vessels, has two cell types, and is also CEA+ (Br J Dermatol 1984;111:175). Glomus tumors with 5+ mitotic figures/50 HPF, atypical mitotic figures, large size (2 cm+), or location deep to the muscular fascia may be designated as glomangiosarcoma, with possible metastatic behavior (Appl Immunohistochem Mol Morphol 2009;17:264).
Glomus tumors without atypia and without mitotic activity typically have a benign clinical course, and excision is curative.
Nat Pernick, M.D., President
and Palak Thakore, Associate Medical Editor
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