title: The value of immunohistochemistry in atypical cutaneous fibrous histiocytoma.
abstract: Atypical cutaneous fibrous histiocytoma is a rare variant of dermatofibroma/fibrous histiocytoma characterized by striking atypia, thus resembling atypical fibroxanthoma. We studied 9 examples of ACFH histopathologically and immunohistochemically to investigate the nature of these atypical cells. Histology revealed ill-defined skin nodules, which were polypoid in 6 cases. A minority of mononuclear and giant cells (< 5%) revealed striking pleomorphism and showed large nuclei with prominent nucleoli. Immunohistologically, the atypical cells expressed vimentin, but were negative for S-100 protein, the keratin marker MNF116, alpha smooth muscle actin, CD34, factor XIIIa, and monocyte/macrophage markers Ki-M1p, KP1 (CD68), and MAC387. Positivity for MiB1 was very modest (< 1%) and limited to small- and medium-sized, inconspicuous cells. Multinucleate giant cells proved to be heterogenous, on one hand cells with differentiation toward macrophages with positivity for Ki-M1p and KP1, on the other toward fibroblasts positive for vimentin only. These immuno-histochemical results for differentiation markers in atypical cutaneous fibrous histiocytoma are similar to our previous findings and data in atypical fibroxanthoma; MiB1 helps to separate these entities from each other as the latter shows a very high proportion of proliferative atypical cells corresponding to the numerous mitoses seen in routine sections.
authors.affiliation: Dermatohistological Private Laboratory, Postfach 4145, D-90021 Nürnberg, Germany. dr.michael.wilk@web.de
authors.forename: Michael
authors.initials: M
authors.lastname: Wilk
authors.forename: Bettina G
authors.initials: BG
authors.lastname: Zelger
authors.forename: Martin
authors.initials: M
authors.lastname: Nilles
authors.forename: Bernhard
authors.initials: B
authors.lastname: Zelger
mesh_terms: D000328:Adult; D014408:Biomarkers, Tumor / Q000032:analysis*; D003937:Diagnosis, Differential; D005260:Female; D018219:Histiocytoma, Benign Fibrous / Q000378:metabolism* / Q000473:pathology*; D006801:Humans; D007150:Immunohistochemistry; D019394:Ki-67 Antigen / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D012878:Skin Neoplasms / Q000378:metabolism* / Q000473:pathology*
chemical_list: D014408:Biomarkers, Tumor; D019394:Ki-67 Antigen