Predictors of Malignant Pathology and the Role of Trans-Thoracic Needle Biopsy in Management of Solitary Fibrous Tumors of the Pleura: A 30-Year Review of a Tertiary Care Center Patient Cohort

Background: Solitary fibrous tumors of the pleura (SFTP) are rare neoplasms with unpredictable behavior. Lack of unifying criteria for benign or malignant SFTP has resulted in reports of SFTP exhibiting malignant behavior years after complete surgical resection (despite benign initial diagnosis). Additionally, the role of trans-thoracic needle biopsy in initial management of SFTP is unclear. Understanding predictors of malignancy identifies patients at unacceptably high risk for non-surgical primary therapy, and for recurrence despite complete surgical resection. Objectives: The primary objectives were to identify clinicopathological predictors of malignancy & recurrence in SFTP. The secondary aim was to determine the role of trans-thoracic needle biopsy in the management decision algorithm of SFTP. Methods: Retrospective chart review was conducted (Jan. 1983-Dec. 2013) at the Ottawa Hospital for pathologically confirmed SFTP. Data were collected on biopsy-related, clinical, histopathological & immunohistochemistry (IHC) variables. Appropriate tests of statistical inference were conducted for all variables. Results: Pathologically confirmed SFTP was identified in 26 cases. Transthoracic needle biopsy was conducted in 22 (84.6%); with 16 (72.7%) biopsies diagnostic of SFTP with IHC; 3 (13.6%) being malignant. Primary management was surveillance in 3 and complete surgical resection in 23. Surgical pathology reported 15 (65.2%) benign and 8 (34.8%) malignant cases. Local recurrence occurred in 3 and distant recurrence in 1. Initial pathology was benign in 3 (75%) with recurrence. Clinicopathologic variables analyzed did not predict recurrent disease. IHC features did not differ between malignant & benign pathology significantly. Predictors of malignant pathology included: infiltrative cellular pattern (p = 0.042), nuclear crowding (p = 0.006), tumour necrosis (p 4 mitoses/ 10 high power field (p < 0.003). Conclusion: Because numerous variables analyzed did not predict recurrent disease, long-term follow-up is warranted regardless of benign or malignant initial histology. Histologic not IHC features predicted malignant pathology. Trans-thoracic needle biopsy did identify malignant SFTP; however its main use should be to differentiate SFTP from other pleural neoplasms using IHC.