Positive MITF and NKI/C3 Expression in Cellular Neurothekeoma and Dermatofibroma.

ABSTRACT

BACKGROUND: Cellular neurothekeoma (CNT) is a benign mesenchymal tumor with uncertain cellular differentiation. Studies have found evidence of myofibroblastic differentiation and possible relation to dermatofibromas (DFs). As microphthalmia transcription factor (MITF) and NKI/C3 stains are routinely positive in CNT, we compared expression patterns of both markers in CNT and DF to assess their relationship. MATERIALS AND METHODS: We assessed cases of CNT (n=25) and DFs (n=35) for histopathologic characteristics and MITF and NKI/C3 expression. Immunostaining results were classified as negative, focally positive (<50%), and diffusely positive (>50%). At least 1 additional melanocytic marker was assessed in each case of CNT. RESULTS: Both DFs and CNTs showed a female predilection and a wide age range. Immunostaining in CNTs for MITF was positive in the vast majority (focal 68%, diffuse 24%), as was NKI/C3 (focal 72%, diffuse 24%). All DFs were MITF positive (diffuse 74%, focal 26%), and most DFs were NKI/C3 positive (focal 57%, diffuse 3%). CONCLUSION: CNT and DF share demographic, histopathologic, and immunohistochemical features, including shared expression of MITF and NKI/C3, especially cellular DF.