Neurofibroma of the Colon: A Diagnostic Mimicker of Gastrointestinal Stromal Tumor.

Gastrointestinal neurofibroma usually develops as diffuse gastrointestinal involvement in neurofibromatosis type 1 patients. Only 4 cases of sporadic colonic neurofibroma in a patient without neurofibromatosis type 1 have been reported in the English literature. A 26-year-old female patient underwent colonoscopy, and a 4-cm-sized polypoid mass was identified in the sigmoid colon. Wedge resection of the mass showed a yellowish, hard submucosal tumor. Microscopically, the tumor was composed of wavy spindle cells, fibroblasts, and strands of collagen; the stroma showed scattered myxoid areas. The differential diagnoses included gastrointestinal stromal tumor, schwannoma, and neurofibroma. Immunohistochemistry for c-Kit, DOG (discovered on gastrointestinal stromal tumors)-1, smooth muscle actin, S-100 protein, and CD34 was performed. The tumor cells were diffusely positive for CD34 and S-100 protein, while they were completely negative for c-Kit, DOG-1, and smooth muscle actin. The final diagnosis was neurofibroma. Sporadic colonic neurofibroma is very rare. Given the diffuse positivity for CD34 and its rarity, colonic neurofibroma can be easily misdiagnosed as gastrointestinal stromal tumor. Recognition of this entity would be beneficial for pathologists to avoid misdiagnosis and unnecessary treatment.