Malignant granular cell tumor of the ulnar nerve: A case report of long-term follow-up and literature review

Background: The incidence of malignant granular cell tumor, an extremely rare Schwann cell-derived tumor with a poor prognosis, is reported to be approximately 0.2% of malignant soft tissue tumors. We report a case of a malignant granular cell tumor originating from the ulnar nerve.Case presentation: A 71-year-old woman presented with a mass in her right forearm. Magnetic resonance imaging showed a tumor with homogenous intensity of T1 and heterogeneous hyperintensity of T2, continuous with the ulnar nerve. Incisional biopsy revealed a malignant granular cell tumor, and marginal excision of the tumor was performed. Histologically, the tumor size was 9.2 cm and consisted of eosinophilic, granular polygonal to round and spindle-shaped cells, with vesicular and prominent nucleoli, and increased mitosis. Immunohistochemically, the tumor cells were positive for S-100 protein, CD68, H3K27me3, TFE3, and SOX10 and negative for smooth muscle alpha-actin, desmin, cytokeratin AE1/3, epithelial membrane antigen, and synaptophysin. The Ki-67 positivity rate was 12%. These findings were consistent with those of malignant granular cell tumors. In addition, no metastasis or recurrence was observed 15 years after the excision.Conclusion: Surgical resection is the standard treatment option. In our case, the diagnostic criteria for malignant granular cell tumors were histologically met. Patients with malignant granular cell tumors have a poor prognosis. However, no metastasis or recurrence was observed in this case 15 years after the surgery.