Significance of fusion status, Oberlin risk factors, local and maintenance treatment in pediatric and adolescent patients with metastatic rhabdomyosarcoma: Data of the European Soft Tissue Sarcoma Registry SoTiSaR

Background Outcome of primary metastatic rhabdomyosarcoma (RMS) is poor. Certain risk factors as fusion status, Oberlin score, and local treatment of primary tumor are known to influence prognosis. Procedure Patients with metastatic RMS were treated according to Cooperative Weichteilsarkom Studiengruppe (CWS) guidance with chemotherapy (CHT), radiotherapy (RT) excluding total lung irradiation (TLI), complete resection of the primary tumor, and metastasectomy if possible. Kaplan–Meier estimators and Cox proportional hazard models were used to examine event‐free survival (EFS) and overall survival (OS) involving also landmark analyses. Results In the European Soft Tissue Sarcoma Registry SoTiSaR (2009–2018), 211 patients were analyzed. Many patients had fusion‐positive alveolar RMS (n = 83; 39%). Median age was 9.4 years [0.1–19.7 years]. Treatment primarily consisted of CHT with CEVAIE (carboplatin, epirubicine, vincristine, actinomycin‐D, ifosfamide, etoposide: 86%, other regimens: 14%), RT (71%), resection of primary tumor (37%), metastasectomy (19%), and lymph node sampling/dissection (21%). Maintenance treatment (MT) (oral trofosfamide, idarubicin, etoposide) was added in 74% of patients. Oberlin factors, fusion status, and MT were predictive for EFS and OS. MT with O‐TIE was not improving outcome when adjusting for the immortal time bias. Local treatment of the primary tumor and radical irradiation (except TLI) improved EFS, not OS, when adjusting for the Oberlin score. Patients with fusion‐negative alveolar RMS (n = 9) had an excellent outcome with a 5‐year EFS and OS of 100%, compared to patients with embryonal RMS (49%/62%), PAX7‐ (22%/47%) and PAX3/FOXO1‐positive ARMS (10/13%), respectively (p