Patients with metastatic rhabdomyosarcoma (RMS), except those younger than 10 years with embryonal RMS, have an estimated long-term event-free survival (EFS) of less than 20%. The main goal of this study was to improve outcome of patients with metastatic RMS by dose intensification with interval compression, use of the most active agents determined in phase II window studies, and use of irinotecan as a radiation sensitizer.

Patients with metastatic RMS received 54 weeks of therapy: blocks of therapy with vincristine/irinotecan (weeks 1 to 6, 20 to 25, and 47 to 52), interval compression with vincristine/doxorubicin/cyclophosphamide alternating with etoposide/ifosfamide (weeks 7 to 19 and 26 to 34), and vincristine/dactinomycin/cyclophosphamide (weeks 38 to 46). Radiation therapy occurred at weeks 20 to 25 (primary) but was also permitted at weeks 1 to 6 (for intracranial or paraspinal extension) and weeks 47 to 52 (for extensive metastatic sites).

One hundred nine eligible patients were enrolled, with a median follow-up of surviving patients of 3.8 years (3-year EFS for all patients, 38% [95% CI, 29% to 48%]; survival, 56% [95% CI, 46% to 66%]). Patients with one or no Oberlin risk factor (age > 10 years or < 1 year, unfavorable primary site of disease, ≥ three metastatic sites, and bone or bone marrow involvement) had a 3-year EFS of 69% (95% CI, 52% to 82%); high-risk patients with two or more risk factors had a 3-year EFS of 20% (95% CI, 11% to 30%). Toxicity was similar to that on prior RMS studies.

Patients with metastatic RMS with one or no Oberlin risk factor had an improved 3-year EFS of 69% on ARST0431 compared with an historical cohort from pooled European and US studies; those with two or more risk factors have a dismal prognosis, and new approaches are needed for this very-high-risk group.