Risk of radiation-related subsequent malignant tumors in survivors of Ewing's sarcoma.

Twenty-four long-term survivors of Ewing's sarcoma were identified as being at risk for a second primary tumor. Among this group of patients followed from 3 to 22 years, 4 new bone tumors were observed, whereas 1.2 x 10(-3) were expected. All new tumors arose in heavily irradiated areas. The risk associated with radiation after 3 years was 7.2 cases/million person-years per rad. The cumulative cancer risk over 10 years for irradiated patients was 35% (SE, 15.1%). Intensive chemotherapy (cyclophosphamide and vincristine administered in five or more courses) seemed to exert an enhancing effect, increasing the rate of development of new tumors.