Abstract

Glomangiosarcoma (malignant glomus tumor) is a very rare tumor of skin and soft tissue which may act aggressively or metastasize. Herein we present a case of a 30-year-old woman with a 2.0 cm red-blue nodule overlying the right popliteal fossa. The mass was exquisitely tender to palpation. The excisional biopsy specimen revealed an irregular rubbery yellow-brown cut surface. Histologic examination showed a well-circumscribed multi-nodular tumor extending from superficial dermis into subcutaneous tissue which, overall, resembled benign glomus tumor. Centrally within a deeper tumor lobule, however, was an enlarged cystic space surrounded by more densely-packed tumor cells with clear cell change and cytoplasmic vacuoles. These cells appeared somewhat larger with irregular nuclei and observed mitotic figures, up to 4-5 per high power field with occasional atypical forms. Tumor cells were highlighted by SMA and MSA and were negative for CD34, CD31, and Pan-keratin immunohistochemistry. Ki67 showed a markedly increased proliferative index within the central cellular nodule compared to surrounding glomus tumor. Although quite focal, this atypical tumor focus was considered consistent with early/evolving glomangiosarcoma within background glomus tumor. Complete excision of the lesion with referral to oncology service was recommended. This case demonstrates the histologic continuum from benign glomus tumor to glomangiosarcoma. It also hints at a more sinister biologic potential of benign glomus tumors, indicating that complete removal is likely the best course of action in even the most banal of cases.

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