Hybrid peripheral nerve sheath tumors

Purpose: The aim of this study was to evaluate patients formerly diagnosed as neurofibroma and schwannoma in terms of hybrid peripheral nerve sheath tumors (PNSTs) via histopathological and immunohistochemical analysis. Materials and Methods: In this retrospective study, 115 patients formerly diagnosed as either neurofibroma or schwannoma were re-evaluated histopathologically. Among these patients, 32 cases which showed mixed morphology, suspicious for hybrid PNST were included in the study. Immunohistochemically, S100, CD34, EMA and ki67 were performed to these 32 cases, suspicious for hybrid PNST.Results: Based on histopathology, 32 of 115 (27.8%) cases were suspicious for hybrid PNST. By the addition of immunohistochemical staining results; 22 of 32 cases were definitely diagnosed as hybrid PNST; of which 18 (81.8%) as schwannoma-neurofibroma and, 4 (18.2%) cases as schwannoma-perineurioma. Conclusion: Hybrid PNSTs are usually benign and have distinct histopathologic and immunohistochemistry findings. In the literature, rare case reports have described local recurrence and malignant transformation in hybrid PNSTs. Therefore, further studies are needed to demonstrate the pathogenetic and prognostic significance of these tumors. Because of the risk of recurrence and malignancy potential, these tumors should be kept in mind in diagnosis of peripheral nerve sheath tumors.