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.