title: The combination of CD99 and NKX2.2, a transcriptional target of EWSR1-FLI1, is highly specific for the diagnosis of Ewing sarcoma.
abstract: Ewing sarcoma (ES) is a high-grade malignant neoplasm primarily affecting children and young adults. The diagnosis of ES is often difficult because of its broad differential diagnosis comprising a diverse group of small round cell tumors (SRCTs). Although the identification of tumor type-specific fusion genes by molecular testing is the gold standard for the diagnosis of ES, such approaches are not always available in a routine pathology practice. Thus, a reliable immunohistochemical marker is required. A recent study using a limited number of tumor samples has shown that NKX2.2, a putative transcriptional target of EWSR1-FLI1, is a useful marker for the diagnosis of ES. In the present study, the immunohistochemical expression of NKX2.2 was evaluated on 46 genetically confirmed ES and 85 non-ES SRCTs, together with comparative assessment of CD99 and other molecular targets of EWSR1-FLI1, including NR0B1, E2F3, and EZH2. NKX2.2 was expressed in 37 (80 %) of the ES samples with a mostly diffuse and strong staining pattern, and 14 (16 %) of the non-ES SRCTs, including olfactory neuroblastomas, extraskeletal myxoid chondrosarcoma, mesenchymal chondrosarcoma, small cell carcinomas, and Merkel cell carcinoma, also expressed this marker. The sensitivity and specificity of the NKX2.2 expression in this cohort were 80 and 84 %, respectively. The specificity when combined with CD99 was 98 %, with exceptional expression of both markers in only two non-ES SRCTs, including one case each of mesenchymal chondrosarcoma and small cell carcinoma. NR0B1, E2F3, and EZH2 were less sensitive for specific markers for ES when applied singly or in any combination. In conclusion, the study reinforces that NKX2.2 is a useful immunohistochemical marker for ES, and that the combination of CD99 and NKX2.2 is a powerful diagnostic tool that can differentiate ES from other SRCTs.
authors.affiliation: Department of Pathology and Oncology, School of Medicine, University of Occupational and Environmental Health, 1-1 Iseigaoka, Yahatanishi-ku, Kitakyushu, 807-8555, Japan.
authors.forename: Ryo
authors.initials: R
authors.lastname: Shibuya
authors.forename: Atsuji
authors.initials: A
authors.lastname: Matsuyama
authors.forename: Mitsuhiro
authors.initials: M
authors.lastname: Nakamoto
authors.forename: Eisuke
authors.initials: E
authors.lastname: Shiba
authors.forename: Takahiko
authors.initials: T
authors.lastname: Kasai
authors.forename: Masanori
authors.initials: M
authors.lastname: Hisaoka
mesh_terms: D000071443:12E7 Antigen; D000293:Adolescent; D015703:Antigens, CD / Q000096:biosynthesis*; D014408:Biomarkers, Tumor / Q000096:biosynthesis*; D015815:Cell Adhesion Molecules / Q000096:biosynthesis*; D002648:Child; D000090322:Homeobox Protein Nkx-2.2; D018398:Homeodomain Proteins / Q000096:biosynthesis*; D006801:Humans; D007150:Immunohistochemistry; D009687:Nuclear Proteins; D015514:Oncogene Proteins, Fusion / Q000096:biosynthesis; D012512:Sarcoma, Ewing / Q000175:diagnosis*; D018228:Sarcoma, Small Cell / Q000175:diagnosis; D012680:Sensitivity and Specificity; D014157:Transcription Factors / Q000096:biosynthesis*; D029961:Zebrafish Proteins
chemical_list: D000071443:12E7 Antigen; D015703:Antigens, CD; D014408:Biomarkers, Tumor; C061828:CD99 protein, human; D015815:Cell Adhesion Molecules; D000090322:Homeobox Protein Nkx-2.2; D018398:Homeodomain Proteins; C000715631:NKX2-2 protein, human; D009687:Nuclear Proteins; D015514:Oncogene Proteins, Fusion; D014157:Transcription Factors; D029961:Zebrafish Proteins; C000715630:nkx2.2b protein, zebrafish