Prognostic factors for localized synovial sarcoma are well defined. However, few data exist regarding patients with metastases at diagnosis. Poor outcome is described but the optimal therapeutic regimen remains unclear. Our aim was to assess the outcome, identify prognostic factors, and analyze treatment strategies.

Patients <21 years with synovial sarcoma and primary distant metastases treated in the consecutive prospective European Cooperative Weichteilsarkom Studiengruppe trials 1980-2010 were analyzed.

Twenty-nine of 296 patients had primary metastases. Twenty-seven could be included. Median age was 16.7 years. Primaries were mainly located in the limbs (78%) and 74% were ≥10 cm. Metastases involved the lungs in all patients. Two patients presented with synchronous bone metastases. Sixty-three percent of patients achieved a first remission, whereas only 26% maintained it. Relapses were metastatic with pulmonary metastases in nearly all patients. Five-year event-free survival and overall survival (OS) rates were 26% and 30%, respectively. Prognosis was best for patients with oligometastatic lung metastases (5-year OS probability 85%). Prognosis was worse for patients with multiple bilateral lung metastases (5-year OS 13%) and even poorer for those with concurrent bone metastases. Treatment elements associated with superior survival were adequate local therapy of the primary tumor and, if feasible, for metastases, chemotherapy with an ifosfamide/doxorubicin-based regimen. The use of whole lung irradiation was not correlated with better outcomes.

The overall prognosis of primary metastatic synovial sarcoma is poor. However, individuals with oligometastatic lung metastases had very good chance for long-term survival when treated with adequate multimodal therapy.