Case report
Malignant glomus tumor of the foot with obvious neuroendocrine differentiation: a case report with immunohistochemical studies

Obvious neuroendocrine differentiation has not been reported in glomus tumor. The author herein reports a malignant glomus tumor of the foot showing obvious neuroendocrine differentiation. A 63-year-old woman presented with tumor of the left foot. The tumor was superficially seated, and located in the dermis. It was completely resected with wide margins. It measured 0.7 × 0.7 × 0.6 cm. Microscopically, the tumor was composed of atypical epithelioid cells located around blood vessel-like structures. The epithelioid cells showed relatively clear cytoplasm and severe cellular atypia, and resembled basal cell carcinoma. Focal areas of squamoid differentiation, carcinoid patterns, and neural differentiations were seen. There was no necrosis or atypical mitosis. However, mitotic figures were seen in 16 per 50 high-power-fields (HPF). The hematoxylin and eosin (HE) diagnosis was basosquamous carcinoma. Immunohistochemically, the tumor cells were strongly positive for vimentin, -smooth muscle actin, and neuron-specific enolase. The tumor was focally positive for NCAM, synaptophysin and chromogranin. The blood vessel-like structures had a layer of CD31- and CD34-positive endothelial cells. Tp53 was positive and the Ki-67 labeling index was 23%. The tumor cells were negative for cytokeratin (CK) AE1/3, CK CAM5.2, CK5, CK6, CK7, CK8, CK14, CK18, CK19, CK20, p63, EMA, CEA, CA19-9, desmin, myoglobin, HMB-45, Melan-A, S100 protein, MUC1, MUC2, MUC5AC, and MUC6. Taken together with HE histology, the tumor was labeled as malignant glomus tumor with neuronal differentiation, based on the classification system of Folpe et al. The post-pathological diagnosis whole body examination using CT, MRI, PET, and endoscopies identified no tumors. The patient is now free from tumor and healthy 18 months after the resection.