Epidemiology and survival factors of appendicular myxofibrosarcoma: a SEER-retrospective study.

Background: The low incidence of myxofibrosarcoma (MFS) makes high power studies difficult to perform. Demographic and prognostic factors for MFS and how they differ from all extremity soft tissue sarcomas (STS) are not well understood. The purpose of this study was to characterize a large cohort of patients with MFS and evaluate epidemiologic and survival factors when compared to all STS.

Materials And Methods: We performed a retrospective review of the Surveillance, Epidemiology, and End Results (SEER) database from 2000 to 2015 to identify 1,440 patients diagnosed with MFS and 12,324 with STS. Survival curves were creased using Kaplan-Meier, and Cox regression analyses were performed to identify hazard ratios (HRs).

Results: Overall survival was greater for STS than MFS (79% . 67%). Patients with MFS had a higher average age at diagnosis than STS (62 . 56), and older age was strongly associated with decreased survivorship for MFS (HR = 7.94). A greater proportion of patients under 30 diagnosed with MFS were female when compared to STS (49.6% . 45.4%). The incidence of MFS and STS increased over the 15-year period, with MFS increasing at a greater rate than STS (1.25% . 2.59%). Survival increased for patients diagnosed after 2008 for both STS (9.4%) and MFS (13.2%).

Conclusions: There are differences between patient demographics and survival factors when comparing MFS to all STS. Monitoring changes in demographic and survival trends for rare STS subtypes like MFS is important to improve diagnostic algorithms and treatment options.