[545] Epithelioid Malignant Schwannoma: A Clinicopathological Evaluation of 13 Cases

Rebecca P Shanesmith, Jose C Cardoso, Cyril Fisher, Eduardo Calonje. Tulane Medical Center, New Orleans, LA; St. John's Institute of Dermatology, St. Thomas' Hospital, London, England, United Kingdom; Royal Marsden Hospital, London, England, United Kingdom

Background: Epithelioid MPNST is an uncommon variant of MPNST. These tumors typically are composed of round cells with abundant cytoplasm with a prominent nucleolus. Unlike classical MPNST, which usually stains focally for S-100 protein, epithelioid MPNST or epithelioid malignant schwannoma stains diffusely for S-100 protein in 80% of cases.
Design: Thirteen cases reported as epithelioid MPNST were retrieved from the referral archives of two of the authors (E.C. and C.F.). The histology was reviewed by all of the authors and where immunohistochemical sections were unavailable for review, the results were taken from the original report. Clinical information and follow-up data were requested from the referring pathologists.
Results: Two patients had a history of neurofibromatosis type 1 (NF1). Sex incidence was essentially equal (7 males:6 females) and the majority (62%) of patients were older than 40 years. Six cases presented in the dermis and subcutaneous tissues (superficial), three cases were located in the subcutaneous tissue (deep), and two lesions were located in a deep major nerve. All cases were strongly positive for S-100 protein and negative for other melanocytic markers. EMA was focally positive in two cases and tumor cells were negative for other markers including desmin, smooth-muscle actin and pan-keratin. Six cases were entirely composed of epithelioid cells, while in five cases more than 60% of tumor cells had an epithelioid morphology. Only two cases were composed of a 50% population of spindle cells. In one case there was osteochondroid metaplasia and in a further case bone metaplasia was noted. In all cases tumor cells displayed cytologic atypia, a single prominent basophilic nucleolus and mitotic activity varied from less than one to 8 per mm square. Follow-up information was available in six cases. The latter range from 36 months to 84 months with a median of 54 months. Two patients died due to tumor spread and two patients had recurrence of the lesion. The other two patients are alive with no evidence of a recurrence or distant metastasis.
Conclusions: In conclusion, we report thirteen epithelioid malignant schwannomas with comparable findings to the literature of these lesions being less associated with NF1 patients, strong S-100 expression of the tumor, composition of the tumor with large epithelioid cells with a vesicular nucleus and prominent basophilic nucleolus, and increased mitotic activity.
Category: Dermatopathology

Tuesday, March 20, 2012 9:30 AM

Poster Session III # 87, Tuesday Morning


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