Extrathoracic location and ''borderline'' histology are associated with recurrence of solitary fibrous tumors after surgical resection

Background. Most solitary fibrous tumors (SFTs) are cured by complete resection, but many recurrent and metastatic SFTs do not respond to treatment and are fatal. Malignant histology, defined by England's pathologic criteria, is strongly associated with recurrence, but some benign SFTs still behave aggressively. Several studies have suggested that extrathoracic SFTs have a worse prognosis. We reviewed thoracic and extrathoracic SFTs from our institution to determine if extrathoracic location is associated with recurrence, independent of malignant histology. Methods. With IRB approval, we retrieved patient pathology reports from the Johns Hopkins Surgical Pathology database between 1991 and 2011 and included 83 SFT patients in our analysis. Patient history and outcomes were obtained from the medical record and primary care physicians. Predictors of recurrence were analyzed by univariate and multivariate analysis and survival determined by the Kaplan-Meier method. Results. Of the 83 patients, 59 had extrathoracic SFTs in neurologic (n = 24), extremity or head/neck (n = 13), or visceral/intraabdominal (n = 22) sites. A total of 74 SFTs were classified benign and 9 as malignant. Of the 14 recurrences, 13 occurred in extrathoracic SFTs; only 7 were classified as malignant. Multivariate analysis confirmed that malignant histology had the strongest association with recurrence, but extrathoracic location also independently predicted recurrence. A total of 20 benign SFTs possessed 1 or more of England's criteria but to an insufficient degree for malignant classification. These ''borderline'' SFTs were more likely to recur than benign SFTs without these features. Conclusions. Extrathoracic and ''borderline'' SFTs with any of England's criteria have a higher risk of recurrence.