Which patients with rhabdomyosarcoma (RMS) do need radiotherapy (RTX)? The long-term results of the CWS studies -81, -86, -91, and -96.

10005 Background: RTX is an essential therapy modality in the treatment of RMS. However, RTX is associated with severe late effects, therefore the indication and the optimal dose are still a matter of controversy. The stratification for the RTX indication and cumulative dose has been optimized in the consecutive CWS trials. Here we report the long-term results of four consecutive prospective trials. Methods: A total of 998 patients enrolled in the CWS-81, 86, -91 and -96 met the inclusion criteria for this analysis: 1) RMS histology 2) localized tumor (IRS Group I-III) 3) complete RTX data set and 4) follow up of minimum 10 yrs. 171 patients were classified as IRS Group I, 171 as IRS Group II and 656 as IRS Group III. 200 tumors (20%) had alveolar histology (RMA). The indication for RTX and the doses of 32Gy, 40Gy, 45Gy, 48Gy, 50Gy and 54Gy were stratified according to patient and tumor related factors. Results: The 5yrs event free survival (EFS) and overall survival (OS) did not differ between the trials included in the analysis. 630 pts were irradiated (63%).There was no major difference in proportion of irradiated patients between the trials 81-96 (62%, 59%, 71%, 61%). The 5yrs EFS by IRS Groups and RTX vs. no RTX were as follows: IRS I 60% vs. 84%, IRS II 73% vs. 72%, IRS III 62% vs. 57% (n.s.). The 5yrs EFS by RTX dose (32±2Gy vs. > 34Gy) were: IRS II 80% vs. 69%, IRS III 70% vs. 61%. Restricting the analysis to alveolar type: the 5 yrs EFS of patients irradiated with 32±2Gy vs. > 34Gy were as follows: IRS II 50% vs. 59%(n.s.), IRS III 30% vs. 41% (n.s.). There was no difference in EFS when splitting the RMS patients irradiated with > 34Gy into 40Gy vs. 45Gy, vs. 48Gy vs. 50 vs. 54Gy. Conclusions: The stratification criteria for RTX seem to compensate for different risk factors and allowed for reducing the cumulative dose to 32Gy in the lower risk group. However, the proportion of irradiated patients could not be reduced significantly. Further improvement in identification of patients who do not need RTX is needed.