title: A case of giant cell-rich solitary fibrous tumor in the external auditory canal.
abstract: We present a rare case of giant cell-rich solitary fibrous tumor (SFT) arising at the left external auditory canal in a 31-year-old woman. The tumor was well-circumscribed and composed of spindle-shaped cells with abundant collagenous bands. Scattered multinucleate giant cells were observed, some of which lined pseudovascular spaces. Although a focal mild-hypercellular area was observed, mitoses were rare and necrosis was absent. Interstitial mast cells were scattered, especially in the hypercellular area. Immunohistochemically, CD34, vimentin, and Bcl-2 presented diffuse positivity. Moreover, both mononuclear spindle cells and multinucleate cells showed nuclear STAT6 positivity, while NAB2-STAT6 fusion gene could not be detected by reverse transcription polymerase chain reaction using formalin-fixed specimen. These findings suggest the pathological diagnosis of giant cell-rich SFT, previously known as giant cell angiofibroma, which is a rare variant of SFT with multinucleate giant cells and occurs predominantly in orbital region. Although giant cell-rich SFTs of extra-orbital sites have been reported, to our knowledge, this is the first case arising in the external auditory canal. Giant cell-rich SFT should be considered as a differential diagnosis of spindle cell lesion with multinucleate giant cells, and STAT6 immunohistochemistry should be performed to distinguish this rare tumor from other mesenchymal neoplasms.
authors.affiliation: Department of Cancer Pathology, Hokkaido University Graduate School of Medicine, Sapporo, Japan.
authors.forename: Sayaka
authors.initials: S
authors.lastname: Yuzawa
authors.affiliation: Department of Cancer Pathology, Hokkaido University Graduate School of Medicine, Sapporo, Japan.|Department of Diagnostic Pathology, Sapporo Higashi Tokushukai Hospital, Sapporo, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Tanikawa
authors.affiliation: Department of Otorhinolaryngology, Sapporo Higashi Tokushukai Hospital, Sapporo, Japan.
authors.forename: Isamu
authors.initials: I
authors.lastname: Kunibe
authors.affiliation: Department of Translational Pathology, Hokkaido University Graduate School of Medicine, Sapporo, Japan.|Translational Research Laboratory, Hokkaido University Hospital, Clinical Research and Medical Innovation Center, Sapporo, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nishihara
authors.affiliation: Department of Diagnostic Pathology, Sapporo Higashi Tokushukai Hospital, Sapporo, Japan.
authors.forename: Kazuo
authors.initials: K
authors.lastname: Nagashima
authors.affiliation: Department of Cancer Pathology, Hokkaido University Graduate School of Medicine, Sapporo, Japan.|Department of Translational Pathology, Hokkaido University Graduate School of Medicine, Sapporo, Japan.
authors.forename: Shinya
authors.initials: S
authors.lastname: Tanaka
mesh_terms: D000328:Adult; D018322:Angiofibroma / Q000175:diagnosis* / Q000473:pathology; D014408:Biomarkers, Tumor; D004424:Ear Canal / Q000473:pathology*; D005260:Female; D015726:Giant Cells; D006801:Humans; D007150:Immunohistochemistry; D050800:STAT6 Transcription Factor / Q000378:metabolism; D054364:Solitary Fibrous Tumors / Q000175:diagnosis / Q000473:pathology* / Q000503:physiopathology
chemical_list: D014408:Biomarkers, Tumor; D050800:STAT6 Transcription Factor
keywords: NAB2; STAT6; external auditory canal; giant cell angiofibroma; solitary fibrous tumor