title: Myofibroblastic differentiation in atypical fibroxanthomas occurring on sun-exposed skin and in a burn scar: an ultrastructural and immunohistochemical study.
abstract: Herein, we report the investigation of two cases of atypical fibroxanthoma (AFX). One AFX developed within actinically damaged skin, as is typical, while the other developed within a burn scar within non-sun-exposed skin. The two tumors showed almost identical histopathological, immunohistochemical and ultrastructural features. The tumors were composed of pleomorphic spindled, epithelioid, multinucleated and bizarre cells with enlarged atypical nuclei. Most tumor cells expressed vimentin and about 50% expressed CD10. Some tumor cells also expressed α-smooth muscle actin and CD68. However, there was no expression of cytokeratins, p63, S-100 protein, melan-A, HMB 45, desmin, epithelial membrane antigen or CD34. Ultrastructurally, the tumor cells contained myofilaments with dense patches but lacked plasmalemmal caveolae and basal lamina. The most prominent finding was the identification of fibronexus junctions. In addition, there were tumor cells containing numerous lysosomal granules. In conclusion, we clearly showed myofibroblastic differentiation in AFX by electron microscopy. We report also a case of AFX directly developing within a burn scar in the absence of actinic damage.
authors.affiliation: Division of Dermatology, Department of Medicine of Sensory and Motor Organs, Tottori University, 86 Nishi-cho, Yonago 683-8503, Japan. ayama813@grape.med.tottori-u.ac.jp
authors.forename: Ayako
authors.initials: A
authors.lastname: Ito
authors.forename: Nanako
authors.initials: N
authors.lastname: Yamada
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Yoshida
authors.forename: Shinichi
authors.initials: S
authors.lastname: Morino
authors.forename: Osamu
authors.initials: O
authors.lastname: Yamamoto
mesh_terms: D008841:Actin Cytoskeleton / Q000648:ultrastructure; D000369:Aged, 80 and over; D014408:Biomarkers, Tumor / Q000378:metabolism; D002056:Burns / Q000150:complications / Q000473:pathology*; D002467:Cell Nucleus / Q000648:ultrastructure; D002471:Cell Transformation, Neoplastic; D002921:Cicatrix / Q000209:etiology / Q000473:pathology*; D005260:Female; D018219:Histiocytoma, Benign Fibrous / Q000378:metabolism / Q000473:pathology*; D006801:Humans; D008247:Lysosomes / Q000648:ultrastructure; D008297:Male; D058628:Myofibroblasts / Q000378:metabolism / Q000473:pathology*; D015260:Neprilysin / Q000378:metabolism; D012867:Skin / Q000473:pathology / Q000528:radiation effects; D012878:Skin Neoplasms / Q000378:metabolism / Q000473:pathology*; D013472:Sunlight / Q000009:adverse effects; D014746:Vimentin / Q000378:metabolism
chemical_list: D014408:Biomarkers, Tumor; D014746:Vimentin; D015260:Neprilysin