title: FOSL1 immunohistochemistry clarifies the distinction between desmoplastic fibroblastoma and fibroma of tendon sheath.
abstract: OBJECTIVE
  Although desmoplastic fibroblastoma (DFB) and fibroma of tendon sheath (FTS) are well-established entities, they may show overlapping clinicopathological features. In addition, cytogenetic data showing a shared 11q12 rearrangement in a small number of cases suggest a close link between these entities. A recent microarray study revealed up-regulation of FOSL1 mRNA in DFBs with 11q12 rearrangement. The aim of this study was to clarify the relationship between DFB and FTS.
  
  
  RESULTS
  We tested 42 cases diagnosed originally as either DFBs or FTSs for interobserver concordance based on the existing histological criteria and correlated the diagnosis with FOSL1 immunohistochemistry. In addition, FOSL1 gene status was determined by chromogenic in-situ hybridization (CISH). Using joint histological evaluation, 41 of 42 tumours were classified unanimously by three pathologists into 25 DFBs and 16 FTSs, whereas only one case received discordant opinions. Immunohistochemically, all DFBs showed diffuse, strong FOSL1 nuclear immunoreactivity (25 of 25, 100%), while none of the FTSs showed such overexpression. None of the selected 42 DFB mimics overexpressed FOSL1. FOSL1 was not rearranged in seven DFBs tested by CISH.
  
  
  CONCLUSIONS
  We confirm here that DFB and FTS are two distinct entities that can be distinguished using the existing histological criteria. This distinction corresponds perfectly with FOSL1 immunohistochemical expression status, and diffuse strong FOSL1 expression specific to DFBs sharpens the border between the two categories. FOSL1 overexpression in DFB may not be caused directly by FOSL1 gene rearrangement. FOSL1 may also be a diagnostic aid for differentiating DFB from other histological mimics.
authors.affiliation: Department of Pathology, Tokyo Metropolitan Cancer and Infectious Diseases Center Komagome Hospital, Tokyo, Japan.|Department of Molecular Pathology, Yokohama City University School of Medicine, Yokohama, Japan.
authors.forename: Ikuma
authors.initials: I
authors.lastname: Kato
authors.affiliation: Department of Pathology and Clinical Laboratories, National Cancer Center Central Hospital, Tokyo, Japan.|Rare Cancer Center, National Cancer Center Hospital, Tokyo, Japan.
authors.forename: Akihiko
authors.initials: A
authors.lastname: Yoshida
authors.affiliation: Department of Orthopaedic Surgery and Musculoskeletal Oncology, Tokyo Metropolitan Cancer and Infectious Diseases Center Komagome Hospital, Tokyo, Japan.
authors.forename: Masachika
authors.initials: M
authors.lastname: Ikegami
authors.affiliation: Department of Orthopaedic Surgery and Musculoskeletal Oncology, Tokyo Metropolitan Cancer and Infectious Diseases Center Komagome Hospital, Tokyo, Japan.
authors.forename: Tomotake
authors.initials: T
authors.lastname: Okuma
authors.affiliation: Department of Pathology, Tokyo Metropolitan Cancer and Infectious Diseases Center Komagome Hospital, Tokyo, Japan.
authors.forename: Akiko
authors.initials: A
authors.lastname: Tonooka
authors.affiliation: Department of Pathology, Tokyo Metropolitan Cancer and Infectious Diseases Center Komagome Hospital, Tokyo, Japan.
authors.forename: Shinichiro
authors.initials: S
authors.lastname: Horiguchi
authors.affiliation: Department of Pathology, Tokyo Metropolitan Cancer and Infectious Diseases Center Komagome Hospital, Tokyo, Japan.
authors.forename: Nobuaki
authors.initials: N
authors.lastname: Funata
authors.affiliation: Rare Cancer Center, National Cancer Center Hospital, Tokyo, Japan.|Department of Musculoskeletal Oncology, National Cancer Center Central Hospital, Tokyo, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Kawai
authors.affiliation: Department of Orthopaedic Surgery and Musculoskeletal Oncology, Tokyo Metropolitan Cancer and Infectious Diseases Center Komagome Hospital, Tokyo, Japan.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Goto
authors.affiliation: Department of Pathology, Tokyo Metropolitan Cancer and Infectious Diseases Center Komagome Hospital, Tokyo, Japan.
authors.forename: Tsunekazu
authors.initials: T
authors.lastname: Hishima
authors.affiliation: Department of Molecular Pathology, Yokohama City University School of Medicine, Yokohama, Japan.
authors.forename: Ichiro
authors.initials: I
authors.lastname: Aoki
authors.affiliation: Department of Pathology, Tokyo Metropolitan Cancer and Infectious Diseases Center Komagome Hospital, Tokyo, Japan.
authors.forename: Toru
authors.initials: T
authors.lastname: Motoi
mesh_terms: D000328:Adult; D000368:Aged; D014408:Biomarkers, Tumor / Q000032:analysis*; D003937:Diagnosis, Differential; D005260:Female; D005350:Fibroma / Q000175:diagnosis* / Q000473:pathology; D006801:Humans; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D008297:Male; D008875:Middle Aged; D047708:Myofibroma / Q000175:diagnosis* / Q000473:pathology; D016760:Proto-Oncogene Proteins c-fos / Q000032:analysis / Q000096:biosynthesis*; D012983:Soft Tissue Neoplasms / Q000175:diagnosis / Q000473:pathology; D013710:Tendons / Q000473:pathology*; D000099169:Fos-Related Antigen 1
chemical_list: D014408:Biomarkers, Tumor; D016760:Proto-Oncogene Proteins c-fos; D000099169:Fos-Related Antigen 1
keywords: FOSL1; chromogenic in-situ hybridization; desmoplastic fibroblastoma; fibroma of tendon sheath; immunohistochemistry