The Impact of Radiation Therapy in Children and Adolescents With Metastatic Rhabdomyosarcoma.

Cameron AL, Elze MC, Casanova M, Geoerger B, Gaze MN, Minard-Colin V, McHugh K, van Rijn RR, Kelsey A, Martelli H, Mandeville H, Bisogno G, Lowis S, Ronghe M, Orbach D, Guizani C, Fürst-Recktenwald S, Chisholm JC, Merks JHM,European Paediatric Soft Tissue Sarcoma Study Group (EpSSG) and the European Innovative Therapies for Children with Cancer (ITCC) Consortium. Int J Radiat Oncol Biol Phys. 2021 Jul 1:S0360-3016(21)00823-3. doi: 10.1016/j.ijrobp.2021.06.031. Online ahead of print.

Purpose: There is limited evidence to define the role of radiation therapy in children with metastatic rhabdomyosarcoma (mRMS). In the international BERNIE study, children with mRMS or non-RMS soft tissue sarcoma were randomized to receive standard chemotherapy with or without bevacizumab, with radiation therapy to all disease sites recommended after chemotherapy cycle 6. We retrospectively evaluated the impact of radiation therapy on survival in the mRMS cohort.

Methods and materials: Patients were grouped according to the radiation therapy they received: radical, partial, or none. Radical irradiation was defined as radiation therapy delivered to all disease sites, unless a site was completely surgically resected. Partial irradiation was defined as radiation therapy to ≥1, but not all, disease sites. Landmark analysis excluded patients with an event before day 221. Overall survival (OS) and event-free survival (EFS) were modeled using Cox proportional hazards models.

Results: Of 102 patients with mRMS, 97 were included in the analysis for OS and 85 for EFS. Overall, 27 patients received radical irradiation, 46 partial irradiation, and 24 no irradiation. EFS was not significantly different among patient groups after adjustment for prognostic factors (hazard ratio [HR] = 0.520; P = .054 for any vs no irradiation). Radiation therapy was associated with improved OS compared with no radiation therapy (adjusted HR = 0.249; P = .00025), with OS being greater for radical versus partial irradiation (HR = 0.245; P = .039). The 3-year OS rate was 84%, 54%, and 23% for patients receiving radical, partial, and no irradiation, respectively. Radical treatment (surgery, irradiation, or both) of the primary site improved EFS and OS compared with no treatment.

Conclusions: These findings demonstrate variability in the application of radiation therapy for mRMS and support the routine use of radical treatment to the primary site. Radical irradiation to metastatic sites may further improve OS. The burden of such treatment should be balanced against prognosis; further studies are needed.