Prognosis of children and young adults with newly diagnosed rhabdomyosarcoma metastatic to bone marrow treated on Children's Oncology Group studies

Background: Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children. Metastatic disease occurs in 16% of all RMS cases and has a poor prognosis. There are limited studies examining the outcomes specific to patients with RMS metastatic to bone marrow despite an incidence of 6% at diagnosis. Our study aims to document the outcomes, prognostic factors, and clinical courses of children presenting with RMS metastatic to bone marrow treated on Children's Oncology Group (COG) cooperative trials.

Methods: We performed a retrospective analysis of the patients diagnosed with RMS metastatic to bone marrow between 1997 and 2013 enrolled on one of four COG RMS clinical trials of D9802, D9803, ARST0431, and ARST08P1.

Results: We identified 179 cases with RMS metastatic to bone marrow. Patients had a median age of 14.8 years, 58% were male, predominantly alveolar histology (76%), extremity was the most common primary site (32%), and 87% had metastatic disease to additional sites; 83% (n = 149) received radiation as a treatment modality. The 3- and 5-year event-free survival was 9.4% and 8.2%, respectively. The 3- and 5-year overall survival was 26.1% and 12.6%, respectively. Age ≥10 years, alveolar histology, FOXO1 fusion presence, unfavorable primary location, higher Oberlin score, and lack of radiation were identified as poor prognostic/predictive characteristics.

Conclusions: This study represents the largest analysis of RMS metastatic to bone marrow, defining the poor prognostic outcome for these patients. These patients may be eligible for therapy deintensification or early pursuit of novel treatments/approaches that are desperately needed.