Clinicopathologic Features of Retroperitoneal Malignant Solitary Fibrous Tumors

We aimed to explore the clinicopathologic and histologic characteristics, as well as the (differential) diagnosis of retroperitoneal malignant solitary fibrous tumors (RMSFTs) in this study. Nine cases of RMSFTs were recruited and identified by an experienced pathologist from the Pathology Department of Beijing Shijitan Hospital. Clinical information was extracted from medical records and obtained by phone calls. A systematic review of published literature on RMSFTs was conducted using PubMed. A pre-specified search strategy was adopted using the key words "solitary fibrous tumor" and "retroperitoneum." Case reports and literature published in the China Academic Journals (CNKI) and WAN FANG databases were also included. In total, 58 patients (33 males and 25 females) were included; their age ranged from 17 to 83 years, with a median age of 52 years. The tumor size ranged from 4 to 36 cm, and most patients had abdominal masses and pain. Of these patients, 56 underwent surgical resection, and two patients died and underwent an autopsy. All patients were followed up for up to 288 months (with a median follow-up of 36 months). RMSFTs are extremely rare. Their diagnosis mainly relies on the histological morphology and the expression profiles of a panel of pathologic molecules measured by immunohistochemistry. Diagnosis of RMSFTs is usually based on the expression of biomarkers such as vimentin, CD34, Bcl-2, CD99, and STAT6. Differential diagnosis includes spindle-shaped cell tumors, such as schwannoma, gastrointestinal stromal tumors, dermatofibrosarcoma protuberans, synovial sarcoma, malignant peripheral nerve sheath tumors, and fibrosarcoma. RMSFTs are prone to recur and even metastasize. Complete resection remains a major treatment, and close follow-up is highly recommended.