Cellular neurothekeoma: Report of two cases with unusual immunohistochemical features.

Cellular neurothekeoma (CNT) is a dermal lesion with still unknown histogenesis, characterized by immunohistochemical staining for NKI/C3, NSE, MiTF, CD10 and CD68, whereas S100 protein, desmin and cytokeratins are negative. Particularly, in several studies NKI/C3 has been reported as a strong marker of CNT. We describe herein the clinical, histopathological and immunohistochemical features of two cases morphologically consistent with myxoid CNT, one of which showing some atypical features, both characterized by negative immunohistochemical staining for NKI/C3. Our findings stress the importance of morphology in diagnosing CNT and underline the fact that NKI/C3 can fail to stain cases belonging to the "neurothekeoma family." In selected cases of CNT, an expanded immunohistochemical panel is mandatory to differentiate this tumor from other dermal lesions.