Does synovial sarcoma grade predict oncologic outcomes, and does a low-grade variant exist?

Background and Objectives While historically aggressive, some synovial sarcomas (SS) are clinically indolent. This study sought to determine whether SS grade predicts oncologic outcomes and whether Grade 1 disease might exist. Methods Thirty-five cases from 2010 to 2019 were retrospectively reviewed. Clinicopathological data were analyzed and Kaplan-Meier assessed survival. Results The median patient age was 37 years (interquartile range: 28-51.5). The local control rate was 74.3%, and recurrence-free survival (RFS) was worse in positive versus negative margin resections (p = 0.023). The incidence of metastasis was 21.9% (n = 7) at a median 31 +/- 31.7 months, and metastasis-free survival was 50.0% in Grade 3 SS versus 86.5% in Grade 2 (p = 0.026). Among a theoretical Grade 1 group, the overall survival (OS) and RFS profiles were improved compared to Grade 2 and 3 SS, respectively (p = 0.014 and p = 0.030). The Grade 1 group had a 15.8% (n = 3) metastatic rate and 80% 10-year survival. Conclusions Tumor grade appears to predict outcomes in SS. A theoretical Grade 1 group showed improved OS and RFS versus Grades 2 and 3 SS, with metastatic rates and long-term survival resembling the historical literature for other low-grade soft tissue sarcomas. Our group continues to support the French Federation of Cancer Centers diagnostic strategy and NCCN treatment guidelines for SS.