Microphthalmia transcription factor and NKI/C3 expression in cellular neurothekeoma.

While the usual or myxoid-type neurothekeoma has been reasonably well established as being a tumor of neural origin, the cellular neurothekeoma remains in disputed histogenesis. We studied a series of 11 cellular neurothekeomas using paraffin immunoperoxidase staining with microphthalmia transcription factor (Mitf), NKI/C3, and S-100. The majority of the tumors in our series stained with NKI/C3 (9/11) and Mitf (9/11). All failed to stain with S-100. Furthermore, we divided our series of cellular neurothekeomas according to cytomorphology; tumors demonstrating predominantly spindled morphology, predominantly epithelioid morphology, and mixed spindle and epithelioid morphology. The two tumors that failed to stain with NKI/C3 both demonstrated predominantly spindled morphology. One of the tumors that failed to stain with Mitf showed exclusive spindled morphology, while the other showed mixed morphology (spindle and epithelioid). Two of the tumors, which stained strongly with Mitf, however, showed exclusive epithelioid morphology. This current study furthers the concept that cellular neurothekeoma is a tumor of neuroectodermal origin, and further suggests that it may express some component of melanocytic differentiation.