Outcome of metastatic non-rhabdomyosarcoma soft tissue sarcoma in children and young adults treated on children's oncology group ARST0332 trial.

BACKGROUND

We evaluated clinical characteristics, response to therapy, event-free and overall survival (EFS and OS), patterns of recurrence/progression, and factors associated with survival in patients with metastatic non-rhabdomyosarcoma soft tissue sarcoma (NRSTS) treated on the Children's Oncology Group ARST0332 trial.

METHODS

All patients with metastatic disease enrolled in ARST0332 were included. Treatment involved multimodal therapy with ifosfamide and doxorubicin, surgery ± radiotherapy. EFS was time from enrollment to progression, recurrence, second malignancy, or death; OS was defined as the time to death from any cause.

RESULTS

The analysis included 80 patients, with synovial sarcoma as the most common histology (n = 21, 26%). Two-thirds of patients (n = 60) had >1 metastatic site, with the lung being the most common site of metastasis. At the week 13 therapy timepoint, response rate [complete or partial response (CR/PR)] was 41%, and 11% of patients had progressive disease. At a median follow-up of 7.5 years, 61 patients had relapse or progression, most commonly occurring at metastatic sites present at diagnosis (41%), followed by new metastatic sites (11%). The 5-year EFS and OS were 21% [95% Confidence Intervals (CI), 11 to 31] and 36% (95% CI, 24 to 47), respectively. In univariable analysis, histologic subtype was associated with EFS, whereas having a single metastatic site and achieving CR or PR at week 13 were associated with improved EFS and OS (p < 0.05).

CONCLUSION

Survival of pediatric metastatic NRSTS remained dismal on ARST0332. Prognosis varied by histology, metastatic burden, and early treatment response, underscoring the urgent need for novel biologically informed, response-adapted treatment strategies.