title: STAT6 immunohistochemistry is helpful in the diagnosis of solitary fibrous tumors.
abstract: Solitary fibrous tumor (SFT) is an uncommon fibroblastic neoplasm. Although histologic characteristics and frequent CD34 expression allow for an accurate diagnosis in the majority of SFT cases, a wide histologic spectrum and an occasional unexpected immunophenotype may pose diagnostic challenges. Molecular analyses have discovered that almost all SFTs harbor an NAB2-STAT6 fusion gene, which is considered specific to this tumor type. Recent studies have suggested that STAT6 immunohistochemistry is a reliable surrogate for detection of the fusion gene. Our aim was to validate these findings by examining a large number of SFT cases and a broad array of 30 different types of non-SFT tumors. A total of 49 SFTs with a range of histologic characteristics and 159 benign or malignant tumors that can mimic SFTs were retrieved and stained for STAT6. All 49 SFTs (100%) showed STAT6 expression that was restricted in the nucleus, mostly in a diffuse and strong manner, irrespective of the tumor sites and histologic patterns. The staining was uniform in most cases but was heterogenous in about 20% of the cases in which zonal staining attenuation was observed, likely reflecting variability in fixation or tissue ischemia. In contrast, only 4 non-SFT tumors (2.5%) exhibited weak nuclear STAT6 expression, whereas the remaining 155 cases showed no staining or often weak reactivity in both the cytoplasm and the nucleus. Therefore, nuclear STAT6 immunoreactivity is a highly sensitive and specific marker of SFTs and can be helpful when diagnosis is inconclusive by conventional methods.
authors.affiliation: Departments of *Pathology and Clinical Laboratory †Neurosurgery and Neuro-Oncology ‡Musculoskeletal Oncology §Thoracic Surgery, National Cancer Center Hospital, Tokyo, Japan.
authors.forename: Akihiko
authors.initials: A
authors.lastname: Yoshida
authors.forename: Koji
authors.initials: K
authors.lastname: Tsuta
authors.forename: Makoto
authors.initials: M
authors.lastname: Ohno
authors.forename: Masayuki
authors.initials: M
authors.lastname: Yoshida
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Narita
authors.forename: Akira
authors.initials: A
authors.lastname: Kawai
authors.forename: Hisao
authors.initials: H
authors.lastname: Asamura
authors.forename: Ryoji
authors.initials: R
authors.lastname: Kushima
mesh_terms: D014408:Biomarkers, Tumor / Q000032:analysis*; D002467:Cell Nucleus / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D012189:Retrospective Studies; D050800:STAT6 Transcription Factor / Q000032:analysis* / Q000096:biosynthesis; D054364:Solitary Fibrous Tumors / Q000737:chemistry / Q000175:diagnosis* / Q000378:metabolism
chemical_list: D014408:Biomarkers, Tumor; D050800:STAT6 Transcription Factor; C494101:STAT6 protein, human