Objectives: To analyze the treatment outcomes and the effects of adjuvant radiotherapy (RT) in patients with synovial sarcoma (SS).

Materials and Methods: The medical records of 103 patients treated with definitive surgery for SS, with/without RT, from August 1982 to July 2013 were reviewed retrospectively. The median age of the patients was 33 years (range, 5 to 72 y). The most frequent tumor location was the extremities (79 patients, 77%). Seventy-five patients (73%) received adjuvant RT and 26 (25%) did not. The median dose of adjuvant RT was 61.2 Gy (range, 45 to 66.6 Gy).

Results: The median follow-up period was 5.4 years (range, 0.2 to 31.0 y). The 5- and 10-year overall survival rates were 77 % and 65%, respectively. The progression-free survival (PFS) rates at 5 and 10 years were 52% and 43%, respectively. The most common site of initial failure was the lung (24 patients), followed by local recurrence (14 patients). The 5-year local-recurrence-free survival (LRFS) and distant-metastasis-free survival (DMFS) rates were 80% and 63%, respectively. On multivariate analysis, a mitosis count of <10 per 10 high-power fields (HPF) was a significant predictor of better overall survival, PFS, LRFS, and DMFS (P=0.004, <0.001, 0.025, and <0.001, respectively). Adjuvant RT was an additional prognostic factor for better PFS and LRFS (P=0.006 and 0.028, respectively). A positive/uncheckable resection margin was associated with poor prognosis for DMFS (P=0.011). There was no significant difference in LRFS between the higher and lower RT dose groups (<63 Gy group, 89%; ≥63 Gy group, 88%; P=0.772).

Conclusions: The lung and primary site were frequent sites of failure in patients treated with definitive surgery for SS. Adjuvant RT improved LRFS and PFS. Frequent mitotic figures (≥10 mitoses per 10 HPF) were the worst prognostic factor for these patients.