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.

Evaluation of NKX2-2 expression in round cell sarcomas and other tumors with EWSR1 rearrangement: imperfect specificity for Ewing sarcoma

“…Since its identification in gene expression studies, 10 NKX2-2 has been described as a diagnostic immunohistochemical marker for Ewing sarcoma, 11 in a similar manner as DOG1 (ANO1) for gastrointestinal stromal tumor, 20 TLE1 for synovial sarcoma, 21 and MUC4 for low-grade fibromyxoid sarcoma. 22 Two prior studies demonstrated NKX2-2 positivity in 80-93% of Ewing sarcomas; 11,12 however, only cases with classic morphology and EWSR1-FLI1 rearrangements were evaluated. In this study, we examined 40 genetically confirmed Ewing sarcomas, including 4 with atypical large-cell cytomorphology, 4 from uncommon locations (cutaneous and uterine), and 3 with confirmed EWSR1-ERG rearrangements.…”

“…The mechanism underlying NKX2-2 expression in mesenchymal chondrosarcomas is unknown. Although a combination of CD99 and NKX2-2 has been suggested to be highly specific for the diagnosis of Ewing sarcoma, 12 this would not exclude mesenchymal chondrosarcomas, which are often positive for both markers.…”

“…10 In recent times, NKX2-2 has been reported as a diagnostically useful immunohistochemical marker for Ewing sarcoma. 11 In published studies on NKX2-2 expression in Ewing sarcoma, 11,12 only classic Ewing sarcomas with EWSR1-FLI1 rearrangement have been evaluated. It thus remains unclear whether NKX2-2 can be diagnostically useful in atypical Ewing sarcomas, Ewing sarcomas with other gene rearrangements such as EWSR1-ERG, and other Ewing sarcoma-like round cell sarcomas including those with CIC-DUX4 or BCOR-CCNB3 fusion.…”

Explant culture of sarcoma patients' tissue

“…However, it is not excluded that sarcoma cells were suppressed by non-tumor cells such as fibroblasts as often observed in long-term cultures. We therefore investigated the morphology and CD99 expression 29 in these cells ( Figure 5). BX-derived cells grew as loosely attached patches that did not reach confluence.…”

An unusual case of primary cutaneous Ewing sarcoma in an adult

“…Recently, the immunohistochemical expression of NKX2.2, a putative transcriptional target of EWSR1‐FLI1, was evaluated on 46 ES and 85 non‐ES SRCT. They demonstrated a 98% specificity of NKX2.2 when combined with CD99 . Thus, it seems to be a powerful diagnostic tool that can differentiate ES from other SRCT, avoiding molecular analysis, which is costly, laborious, and only available at a limited number of large centers.…”