Refining Risk Stratification and Surveillance Strategies in Pleuropulmonary Solitary Fibrous Tumors-An International, Retrospective, Multicenter Analysis

Background: Solitary fibrous tumor of the pleura are rare neoplasms, and follow-up protocol is lacking. Various risk stratification systems have been proposed to predict recurrence. The aim of this study is to evaluate common risk scores and risk factors leading to a recommendation for follow-up frequency. Methods: We pooled data as part of a multicenter international study with the participation of eight centers in Germany, Switzerland, Denmark, and Austria. Kaplan-Meier survival-curves were used comparing several risk stratification system(s). A Log-rank test was performed to analyze prognostic clinical and pathological factors affecting overall and recurrence-free survival. Results: We included 155 patients from 2004 to 2024: 52.3% were male, median age was 64 years (range 32 to 89). Recurrence rate was 17.4% with median recurrence-free survival of 131 months. Mean time to recurrence was 64.4 (range 9-151) months. Analysis showed that age, tumor morphology, necrosis, and increased mitotic activity were independent prognostic factors for RFS. Conclusions: The WHO risk stratification system demonstrated the highest discriminatory power for recurrence-free survival in the Kaplan-Meier analyses, indicating that the WHO classification remains the most accurate predictor to date. We modified the commonly used risk systems to achieve improved stratification into low-, intermediate- and high-risk groups. The occurrence of late recurrences underscores the need for long-term follow-up.