Curative‐intent radiotherapy for pediatric osteosarcoma: The St. Jude experience

BACKGROUND: Radiation therapy (RT) confers local tumor control and survival advantages in some patients with osteosarcoma, yet pediatric and adolescent and young adult (AYA) population studies are limited. METHODS: Twenty-eight patients treated with curative-intent RT (median dose, 59.4 Gy; range, 40-76 Gy) at our institution from 1990 to 2017 were retrospectively identified. Cumulative incidence (CIN) of local failure (LF) was estimated by Gray's method and overall survival (OS) by the Kaplan-Meier method. Competing-risk regression and Cox proportional hazards models determined predictors of outcome. Toxicity was reported according to CTCAE v4.0. RESULTS: With a median follow-up of 99.1 months in living patients, nine patients (32.1%) developed LF. Estimated CINs of LF with competing risk of death at 5 years for the entire cohort, patients at initial diagnosis (n = 16), and recurrent/refractory patients (n = 12) were 32.7% (95% CI, 16.0-50.5%), 25.0% (95% CI, 7.3-48.0%), and 43.8% (95% CI, 13.6-71.0%), respectively (P  =  0.31). Estimated 5-year OS was 42.6% (95% CI, 23.2-62.0%), 54.6% (95% CI, 29.5-79.6%), and 24.3% (95% CI, 0-52.2%), respectively (P  =  0.15). No clinicopathologic features were significantly associated with LF, yet lack of chemotherapy or metastasis at the time of RT was independent significant prognostic factors of decreased OS. Eleven patients experienced RT-related morbidity, with two grade 3 toxicities and no grade 4/5 events. CONCLUSIONS: Curative-intent RT in pediatric and AYA patients was well tolerated and achieved a local tumor control rate of 75% in patients with primary disease. Local control rates were similar to those in primarily adult studies, with similar or lower doses.