sentences:  Ewing's sarcomas represent 16% of primary bone sarcomas.In the United States, they are most common in the second decade of life, with a rate of 0.3 cases per million in children under 3 years of age, and as high as 4.6 cases per million in adolescents aged 15–19 years.Internationally, the annual incidence rate averages less than 2 cases per million children.