Abstract: Objective　To explore the clinical, pathological, molecular phenotypic characteristics and prognosis of childhood Ewing's sarcoma family tumor (ESFT). Methods　The clinical and pathological data of ESFT in 50 children from August 2008 to December 2018 were analyzed retrospectively. Results　In the 50 children (29 males and 21 females), median age at onset was 8 years (7 days to 14 years) and the median follow-up time was 35 months (1 to 137 months). The first symptom of 23 cases was local pain, 21 cases presented with painless mass (19 cases had mass ≥ 8 cm), and 6 cases presented with lower limb dyskinesia, fever, snoring, etc. Fifteen children had metastasis at initial diagnosis. Immunohistochemistry showed that 100% of the 50 children (50/50) were positive for CD99, 80% (20/25) for FLI-1 and 80% (4/5) for NKX2.2. Thirty-two children (32/35, 91%) had EWSR1 fusion gene translocation. Thirty-two of the 50 children received surgery combined with chemotherapy and radiotherapy. The 3-year overall survival rate (3y-OS) was (68.2±6.9) %, including (78.7±7.2) % in the non-metastatic group and (20.6±16.1) % in the metastatic group (P<0.001). The Log-Rank test results showed that children with no metastasis, tumor <8 cm in diameter, limb being primary, complete resection, combined treatment and combined radiotherapy had a longer survival time, and the differences were statistically significant (P<0.05). Cox regression analysis showed that distant metastasis, incomplete surgical resection and no combination therapy were independent risk factors for poor prognosis of ESFT children (all P<0.05). Conclusions　Combination of EWSR1 gene translocation and CD99, FLI-1, NKX2.2 molecular expression can improve the accuracy of ESFT diagnosis. Distant metastasis, incomplete resection of the mass and failure to receive multidisciplinary treatment at the first diagnosis are the adverse factors of the prognosis of the patients.

Key words: Ewing sarcoma family tumor;　clinical feature;　pathology;　molecular phenotype;　prognosis