Myxofibrosarcoma (fibromyxosarcoma): A population-based analysis of clinicopathological features, treatment patterns, and survival outcomes from the SEER database

Myxofibrosarcoma (fibromyxosarcoma) is one of the most common soft tissue sarcomas in elderly patients, yet population-based data characterizing its epidemiology and outcomes remain limited. This study aimed to characterize the clinicopathological features, treatment patterns, and survival outcomes of fibromyxosarcoma using the Surveillance, Epidemiology, and End Results database. Patients diagnosed with myxofibrosarcoma between 1992 and 2022 were identified from the Surveillance, Epidemiology, and End Results database. Overall survival and cancer-specific survival were estimated using Kaplan-Meier methods. Cox proportional hazards regression identified independent prognostic factors. Competing risks analysis using cumulative incidence functions and Fine-Gray models accounted for non-cancer mortality. A total of 1879 patients were included, with a median age of 64 years and male predominance (53.7%). Age-adjusted incidence increased significantly (annual percent change: 6.4%; 95% confidence interval [CI]: 5.4%-7.5%). The lower extremity was the most common primary site (45.4%), with 51.0% presenting with localized disease. Surgical treatment was performed in 90.5% of patients, and 48.9% received radiotherapy. Five-year overall survival was 74.3% (95% CI: 72.2%-76.5%) and cancer-specific survival was 85.2% (95% CI: 83.4%-87.0%). In multivariate analysis, age was the strongest independent prognostic factor (age 75+ vs <40: hazard ratio: 19.77, 95% CI: 12.10-32.30, P < .001), followed by stage (distant vs localized: hazard ratio: 5.43, 95% CI: 3.66-8.05, P < .001) and grade. Competing risks analysis confirmed these associations with attenuated effect sizes, particularly for age. Myxofibrosarcoma demonstrates favorable intermediate-term survival, particularly for localized extremity tumors in younger patients. Age is the dominant prognostic factor, reflecting both cancer-specific and competing mortality risks. Surgical resection remains the treatment cornerstone; radiotherapy was associated with improved survival in adjusted analyses, though unmeasured confounders (surgical margin status, radiation field and dose, and performance status) preclude causal interpretation. The competing risks framework offers clinically relevant estimates for counseling elderly patients with significant non-cancer mortality risks.