Abstract

Malignant glomus tumor (MGT), also known as glomangiosarcoma, is an exceedingly rare sarcoma with modified smooth muscle glomus cell differentiation that often affects acral cutaneous sites but can also involve viscera. Two main histomorphologic patterns have been described in MGT: fibrosarcoma-like and small round blue cell-like. MIR143(CARMN)-NOTCH1/2/3 gene fusions, as well as BRAF and KRAS mutations, have been recently described in both benign and malignant glomus tumors. We present the case of a 58-year-old male with a MGT involving the skin of the left wrist. The lesion showed prominent ulceration and expansile tumor nodules with a mixture of focal recognizable residual glomus tumor. Benign and symplastic features abruptly transitioned to the malignant cellular component with both fibrosarcoma/myofibroblastic sarcoma-like and small round blue cell-like patterns. The foci with malignant morphology were predominant and showed brisk mitotic activity and complete loss of reticulin fiber network on reticulin histochemical stain. The tumor cells were positive for SMA and negative for Keratin cocktail, Sox10 and p63. A Ki-67 immunostain revealed high proliferative index in the areas with malignant histomorphology. Gene fusion analysis with Archer platform revealed a MIR143(CARMN)-NOTCH2 fusion and failed to reveal BRAF and KRAS mutations. Unfortunately, following the excision of the lesion the patient was lost to follow up. In summary, we present a case of rare cutaneous MGT with both fibrosarcoma/myofibroblastic sarcoma-like and small round blue cell-like histomorphologies that harbored a MIR143(CARMN)-NOTCH2 gene fusion. Although it was not necessary in our case due to the presence of a pre-existing recognizable glomus tumor, demonstration of MIR143(CARMN)-NOTCH1/2/3 gene fusions could aide in the diagnosis of limited small biopsies where only the malignant component is represented.

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