Prognostic implication of SYT-SSX fusion type in synovial sarcoma: A multi-institutional retrospective analysis in Japan

The prognostic implication of SYT-SSX fusion type in synovial sarcomas is still controversial. The aim of this study is to clarify the prognostic impact of fusion type, in association with other clinical factors, in patients with synovial sarcoma in Japan. Data on 108 SYT-SSX fusion transcript-positive patients with synovial sarcoma, treated in 11 tertiary referral cancer centers in Japan, were retrospectively analyzed. The following parameters were examined for their potential prognostic impact: SYT-SSX fusion type, patient age at presentation, sex, primary tumor location, tumor size, histological subtype, histological grade, treatment modalities and disease stage at presentation. Among the patients with localized disease at presentation, 5-year overall survival (OS) for SYT-SSX1 and -2 subgroups were 84.4 and 74.9%, respectively (P=0.244). Five-year metastasis-free survival (MFS) rates were 67.8% for SYT-SSX1 and 68.5% for SYT-SSX2 (P=0.949). Univariate survival analyses for 91 patients with localized disease at presentation showed that tumor size was the only significant prognostic factor for OS (P=0.0033) and MFS (P=0.0029) and the histological grade was marginally significant for MFS (P=0.0785), whereas the SYT-SSX fusion type and other variables were not. Multivariate survival analyses further indicated that tumor size was the most significant independent prognostic factor for OS and MFS and the histological grade was also significant for MFS. In conclusion, the SYT-SSX fusion type is not a significant prognostic factor unlike tumor size, followed by histological grade for patients with localized synovial sarcoma in Japan.