RADIATION-THERAPY FOR RHABDOMYOSARCOMA - LOCAL FAILURE RISK FOR CLINICAL GROUP-III PATIENTS ON INTERGROUP RHABDOMYOSARCOMA STUDY-II

Purpose: A subset of 362 pediatric patients with rhabdomyosarcoma was selected from a total of 532 eligible IRS-II patients in Clinical Grou p III to assess the local and regional failure rates following radioth erapy and to determine patient, tumor, and treatment factors contribut ing to the risk for local and regional failure. Methods and Materials: The study population was selected from all eligible IRS-II Clinical G roup III patients. Excluded patients were those with ''special pelvic' ' primary sites whose protocol management restricted radiotherapy (n = 123), and those who were removed from the study before radiotherapy w as to begin, or because it was omitted (n = 47). A binary recursive pa rtitioning model was used to identify subgroups of the remaining 362 p atients at risk of local or regional failure. Results: The local (only ) failure rate was 17% (95% confidence interval, 13-21%), and the loca l (all) failure rate was 20% (95% confidence interval, 16-24%). The 5- year actuarial risk of local (all) failure was 22% (95% confidence int erval, 18-27%). The risk of regional (nodal) failure was between 2% an d 23%. Increasing tumor size predicted an increased local failure risk . Primary tumors located above the clavicle had a reduced risk of loca l failure. The binary recursive partitioning model identified a subset of patients at high risk of local failure. Those patients had primary tumors in the chest, pelvic region, extremity, or trunk, or tumors > 10 cm in diameter. Their local failure rate was 35% (compared to 15% f or the remaining patients). The subset of patients at high risk for re gional (nodal) failure had node involvement at diagnosis and a primary tumor originating at a site other than orbit, parameningeal, or trunk . Compliance with radiation treatment guidelines approached but did no t achieve statistical significance as a predictive factor for local fa ilure. By univariate analysis, factors not influencing local failure r isk were age, race, gender, adenopathy, and histology. Conclusion: Rad iation therapy and chemotherapy administered to Clinical Group III pat ients entered into the IRS-II protocol produced sustained local contro l in most cases. Knowledge of the factors which predict an increased r isk of local or regional failure will facilitate the design of new tre atment strategies. (C) 1997 Elsevier Science Inc.