摘要目的:探讨儿童骨外尤文肉瘤误诊病例的临床病理学特点、诊断及鉴别诊断，分析病理误诊原因。方法:对2011年1月至2019年7月西安市儿童医院和空军军医大学西京医院病理科诊断的34例骨外尤文肉瘤患儿行回顾性分析，收集6例初次病理误诊的病例行苏木精-伊红染色、免疫组织化学染色，采用荧光原位杂交(FISH)检测 EWSR1基因断裂，观察其临床特征、组织学形态、免疫表型及分子遗传学情况。 结果:6例患儿中位年龄7岁，病初5例表现为无痛性缓慢生长的局限性包块，其中4例位于皮下浅筋膜，1例为迅速增大的软组织肿物。肿瘤细胞呈分叶状、巢片状分布。2例由小蓝圆细胞构成，4例存在形态学变异，表现为细胞体积大，胞质丰富。其中1例核染色质细腻；1例核透亮，可见核仁；1例由上皮样细胞组成；1例为体积较大的圆形、卵圆形细胞混杂梭形细胞、上皮样细胞。CD 99、白血病病毒整合基因1(FLI1)、ERG阳性比例分别为5/6例，5/6例，2/6例。FISH均检测到 EWSR1基因断裂重排。 结论:发病年龄小、位置表浅且初始表现为良性的生物学行为，存在组织学变异和不典型的免疫组织化学标记是儿童骨外尤文肉瘤病理误诊的3个重要因素，因此诊断需结合临床特征、形态学、免疫组织化学染色及 EWSR1基因检测综合考虑。

abstractsObjective:To investigate clinicopathological characteristics of misdiagnosed pediatric extraskeletal Ewing′s sarcoma in children, its diagnosis and differential diagnosis, and the reasons of misdiagnosis by pathologists.Methods:The clinical data of 34 cases of pediatric extraskeletal Ewing′s sarcoma diagnosed by the Department of Pathology, Xi′an Children′ Hospital and Xijing Hospital Fourth Military Medical University from January 2011 to July 2019 were retrospectively analyzed.Hematoxylin-eosin staining, immunohistochemical staining and EWSR1 fusion gene detection by fluorescence in situ hybridization (FISH) were performed on 6 primarily misdiagnosed cases.The clinical features, histological morphology, immunophenotype and molecular genetics of these 6 patients were studied. Results:The median age of 6 cases was 7 years old.There were 5 cases with slowly-growing, painless and localized masses.Four masses were located in the superficial subcutaneous fascia, and 1 was a rapidly growing soft tissue mass.Tumor cells were lobular and nest-like under low power microscopy.At high power microscopy, 2 cases were composed of small blue round cells, and 4 cases had morphological changes, including an increase in cell volume and enriched cytoplasm.Among the 4 cases with tumor morphological changes, tumor cells of 1 case had fine and smooth chromatin, tumor cells of 1 case had clear nuclei and prominent nucleoli, tumor cells of 1 case were composed of epithelioid cells, and tumor cells of 1 case were mixed spindle and epithelioid cells in large round and oval cells.The positive rates of CD 99, friend leukaemia integration-1(FLI1) and ERG were 5/6 cases, 5/6 cases and 2/6 cases, respectively.Rearrangements of EWSR1 gene were detected in all 6 cases. Conclusions:Biological characteristics including young onset age, superficial position and primary benign tumor, histological diversity and atypical immunohistochemical markers are 3 important factors contributing the misdiagnosis of extraskeletal Ewing′s sarcoma in children.The diagnosis should be made by combining the clinical features, morphology, immunohistochemical staining and EWSR1 gene detection.