Solitary fibrous tumor (SFT) is a mesenchymal neoplasm that was originally believed to be of submesothelial origin. These neoplasms have a favorable prognosis and usually originate from the visceral pleura. Rarely, they may occur at various extrapleural sites and show malignant behavior coupled with dedifferentiation. NAB2-STAT6 fusion gene and STAT6 nuclear expression are biomarkers for diagnosis of SFT. Recently, dedifferentiation has been described in rare cases of SFT and it correlates with the aggressiveness of the clinical course. Hence, we report a rare case of retroperitoneal dedifferentiated solitary fibrous tumor.

Case report:

A47 years old male came with chief complaints of presacral mass, bleeding per rectum, and altered bowel habits for 2 months. Trucut Biopsy from presacral mass was done and differential diagnosis of Leiomyosarcoma, Solitary fibrous tumor and synovial sarcoma were given and immunohistochemistry (IHC) was advised. IHC reveals strong nuclear positivity for STAT6, CD34 positive in vessels, negative for SMA and PAN CK. With the above findings, diagnosis of Solitary fibrous tumor was made.

Retroperitoneal Enbloc mass excision with low anterior resection was done and sent for histopathological examination. The final impression of Dedifferentiated solitary fibrous tumor Grade 3 was given.


Dedifferentiated SFT is uncommon, but it appears to have a worse prognosis when compared to conventional SFT. These dedifferentiated regions within the tumor are sharply demarcated from the conventional SFT portion. Hence extensive tissue sampling and utilization of ancillary studies such as immunohistochemistry and molecular studies help in the accurate diagnosis.