Bone sarcomas were the most common SMN reported in a childhood cancer survivor cohort treated between 1940 and 1983 in Great Britain. The overall cumulative risk was approximately 1 % within the 20-year period following the original diagnosis . Patients who have survived Ewing's sarcoma appear to have a cumulative risk between 7-22 % of developing a second bone tumor by 20 years, depending on the cohort studied . Radiation has been implicated as the major predisposing factor, with the risk increasing substantially with increased doses, especially at doses >60Gy [11,32]. Because this dose has not commonly been used during the past two decades for Ewing's sarcoma, the risk should be lower in patients treated during this period. There is also evidence that exposure to the highest doses of radiation (i.e. doses greater than 80Gy - which is not used in any current pediatric regimen) does not carry an excess risk. Presumably, this is secondary to the "cell kill" phenomenon, in which cells with a potential for malignant transformation are killed by the high dose radiation . At the other end of the spectrum, patients exposed to less than 10Gy have no increased risk, or a very small increased risk. The finding by some that alkylating agents, especially cyclophos-phamide, both increase the risk of a secondary bone sarcoma, independent of radiation exposure, and decrease the interval between treatment and the development of an SMN needs to be confirmed [43, 58]. The role of a genetic predisposition combined with therapeutic exposure is not yet fully understood, except in the case of heritable retinoblastoma, where the cumulative risk of SMN, most commonly bone and soft tissue sarcoma, ranges from 10-50%, - or more than 400 times that expected in the general population . Since children with Neurofibro-matosis 1 are prone to the development of primary and secondary sarcomas, radiation should be used only as necessary to effect cure. Careful surveillance of survivors who required radiation is indicated [34,38].
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