Size and Location are the Most Important Risk Factors for Malignant Behavior in Resected Solitary Fibrous Tumors

Purpose. While previously thought to be clinically indolent, recent data suggest significant late metastatic capacity of solitary fibrous tumors (SFTs). We define prognostic factors for recurrence and disease-specific death (DSD) in resected primary SFTs. Methods. Resected primary SFTs from 1982 to 2015 were identified from a prospective, single institutional database. Risk factors for local (LR) and distant recurrence (DR), and DSD were assessed using competing risk analysis. Results. A total of 219 patients with median follow-up of 6.1 (0.1-22) years were included. Five- and 10-year cumulative DSD was 9 and 11%, respectively. Size greater than the median 8 cm, gender, location, and complete gross resection were significantly associated with DSD (p < 0.05). Five- and 10-year cumulative risk (CR) of LR was 4 and 7%, whereas 5- and 10-year CR of DR was 13 and 16%, respectively. LR was associated with location (p = 0.02) and tumor size (p = 0.02), and DR was associated with size (p < 0.01). Histopathologic classification did not predict long-term behavior with both malignant and benign tumors demonstrating capacity for DR and associated death. Tumors in the thoracic cavity and abdomen/retroperitoneum presented the greatest risk of DR (16 and 27% 10-year CR). On multivariate analysis, size >= 8 cm (hazard ratio 2.89, p = 0.05) and tumor location in chest or abdominal/retroperitoneal cavity (hazard ratio 2.68, p = 0.01) significantly impacted DSD. Conclusions. Recurrence is highly associated with DSD and events occur as late as 16 years after initial presentation, including in patients with initially considered benign tumors. Patients with large (>= 8 cm) tumors in the chest or abdominal/retroperitoneal cavity are at greatest risk.