Primary solitary fibrous tumor (SFT) in the retroperitoneum

Solitary fibrous tumor (SFT) is an infrequent but distinct neoplasm, which generally arises from submesothelial connective tissue in the pleura. SFT is rarely recognized in extrathoracic sites, and histologically identical conditions have also been reported in the retroperitoneum, although their pathophysiology has not been extensively investigated.

We present four cases of primary SFT in the retroperitoneum, and review 37 similar cases in the previous literature.

About 40% of patients were asymptomatic, and 19.2% and 15.4% presented with an abdominal mass and urinary symptoms, respectively. The tumor size ranged between 2 and 26 (mean 9.1) cm. Sixty-three percent of tumors showed nonspecific development with haphazard distribution of bland short spindle or polygonal cells with or without collagenous bundles and stromal hyalinization. In 22.0%, hemangiopericytomatous appearance was seen. About 15% of cases showed histologically malignant characteristics. The tumor cells were immunoreactive for vimentin in all cases, CD34 in 91% and Bcl-2 in 86%. All tumors were excised, and in 85.4% of cases, tumors did not recur postoperatively for 6 to 48 months. No significant difference was found between the recurrence rate of histologically benign and malignant cases. Cases positive for both CD34 and Bcl-2 had no recurrence.

The identification of SFT in the retroperitoneum is of importance because histopathological indicators of malignancy are not necessarily associated with clinical malignant potential in many cases of retroperitoneal SFT. Retroperitoneal SFT showing typical pathological features with expression of CD34 and Bcl-2 is associated with a favorable outcome following excision.