Epidemiology, incidence, and survival of synovial sarcoma subtypes: SEER database analysis.

Background: Synovial sarcoma (SyS) is a rare malignancy that is typically located on the limbs and occurs predominantly in adolescents. A study in a large population for SyS comparing subtypes has not yet been reported.
Methods: National Cancer Institute's Surveillance, Epidemiology, and End Results database was queried for patients diagnosed with SyS between January 1975 and December 2016. Patients were classified demographically according to gender, age, race/ethnicity, and marital status, and they were also classified by tumors, subtypes, localization, grade, year of diagnosis, laterality, type of treatment, and follow-up results.
Results: A total of 3228 patients were included, with a mean age of 39.3 ± 18.8 (range: 1-94), of which 1521 (47.1%) were females and 1707 (52.9%) were males. According to its subtypes, 47.2% were SyS not otherwise specified, 32.3% were spindle cell, 19.9% were biphasic, and 0.6% were epithelioid type. The overall survival period is 138.0 (95% confidence interval: 113.2-162.8) months. Survival duration was found to be significantly different between groups according to gender (log-rank test; p < 0.001), age groups (log-rank test; p < 0.001), race (log-rank test; p = 0.001), marital status (log-rank test; p < 0.001), tumor subtypes (log-rank test; p < 0.001), tumor location (log-rank test; p < 0.001), tumor laterality (log-rank test; p < 0.001), date of diagnosis (log-rank test; p = 0.025), tumor grade (log-rank test; p < 0.001), historic stage (log-rank test; p < 0.001), state of chemotherapy (log-rank test; p < 0.001), state of radiotherapy (log-rank test; p < 0.001), presence of metastasis (log-rank test; p < 0.001), and total number of malignant tumors (log-rank test; p < 0.001).
Conclusion: Male gender, being colored individual, being over 35 years at the time of diagnosis, epithelioid type, non-head and neck region localization is associated with poor prognosis. While radiotherapy improves survival, benefit of chemotherapy is unclear.
Level of Evidence: III retrospective analysis.