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.