Abstract

Cutaneous malignant glomus tumors (cMGT) are rare, with fewer than 50 reported to date. We report a cMGT arising in the right elbow in a 35-year-old woman, clinically thought to represent a cyst. Biopsy demonstrated a multinodular proliferation of spindled to ovoid cells with enlarged vesicular nuclei and moderate nuclear pleomorphism extending from the superficial to deep dermis.  Mitoses were 12/10 HPF. No necrosis or lymphovascular invasion was identified. Distinct areas of preexisting benign glomus tumor were also present. Immunohistochemistry was strongly positive for SMA, smooth muscle myosin and there was diffuse pericellular staining for Type IV collagen in both components. No clinical follow up was available, but overall cMGTs have an approximately 15% risk of metastasis, much lower than deep soft tissue MGTs. Clinicopathologic features which predict metastatic risk are poorly understood. Recent reports have identified a CCND3 mutation and MIR143(CARMN)::NOTCH2 fusion in two separate cMGT cases, but what molecular alterations occur in cMGTs as compared to deep soft tissue MGTs is largely unknown and needs additional study.