Cellular neurothekeoma with neuroendocrine differentiation.

We report a case of cellular neurothekeoma with unusual clinicopathological features in which neuroendocrine markers, determined by immunohistochemistry were observed. Histologically, the tumor showed a micronodular architecture with hypercellular lobules composed of slightly spindled to epithelioid cells, with nuclear atypia or pleomorphism and extension into fat, skeletal muscle. Neoplastic cells were immunoreactive for NKI/C3, CD68, CD10, and smooth-muscle actin, whereas S100 and HMB-45 staining was negative. An intriguing feature was the strong expression by tumor cells of different neuroendocrine markers. Clinical follow up showed no local recurrences after five months despite the presence of positive margins. The presence of atypical histopathological features may cause diagnostic problems with malignant mesenchymal tumors, nevo-melanocytic lesions, and fibrohistiocytic tumors. The immunohistochemical profile including the positive staining for neuroendocrine markers may suggest divergent differentiation or an origin from myofibroblast and neuroendocrine cells.