Ewing Sarcoma in Infants and Children Under 2 Years of Age: A French Retrospective Study.

Ewing sarcoma, the second most common primary bone cancer in children, requires intensive treatment that may lead to significant long-term sequelae, particularly in infants. We retrospectively analyzed data from 1621 French patients treated between 1988 and 2015 within the EW88/93/97 or EE99 trials, focusing on 17 infants diagnosed before 24 months of age (1% of the cohort). Their outcomes were compared to the 1245 older pediatric patients (aged 2-18 years). Infant Ewing sarcomas were more frequently extraosseous (29% vs. 8%, p = 0.0037). Acute chemotherapy tolerance was comparable between infants and children under 2 years of age and older children. With a median follow-up of 13.2 years (range: 7.8-15), adapted chemotherapy doses and reduced use of radiotherapy for local treatment, outcomes in infants were favorable, with the same rate of 88% for 5-year disease-free survival (DFS) and overall survival (OS). Two infants experienced localized recurrences, one of whom had undergone incomplete tumor resection without additional local treatment. At the last follow-up, long-term side effects were predominantly associated with local treatments, particularly surgery, rather than chemotherapy. However, given the young age of the patients, certain late toxicities (e.g., fertility impairment) remain unevaluated or could manifest in later years. Adapting chemotherapy doses to age and weight, combined with optimal local treatment, enables high survival rates in infants with Ewing sarcoma. Further monitoring is essential to assess long-term sequelae as this population ages.