Solitary fibrous tumor

Abstract

Solitary fibrous tumor (SFT) is a rare tumor of mesenchymal origin that account for less than 2% of all soft tissue masses. Initially identified in the pleura, SFT has been identified in multiple anatomic locations and can arise anywhere in the body. The varying histologic features along with non-specific means of identification have led SFT to be associated with several different names. Over the last several decades, sustained advances through research and technology have led to more reliable methods for differentiating this distinct soft tissue tumor. Advances specifically in immunohistochemistry and molecular diagnostics have identified CD34 as the most consistent marker in SFT, however even this lacks specificity to conclusively narrow down the broad differential for exact identification. More recently the discovery of the NAB2-STAT6 fusion gene has led to more precise diagnosis of SFT. Like many other soft tissue tumors, surgical management is the mainstay of treatment for SFT with emphasis on obtaining tumor-negative margins. Radiation therapy and chemotherapy regimens have not demonstrated global effectiveness, and thus no standardized treatments have been identified. Given the rarity of SFT and current supportive evidence for therapies, management should be focused on tumor extirpation. Nonetheless, individualized therapy, determined within a multidisciplinary setting should be considered.

Keywords: Solitary fibrous tumors (SFT); hemangiopericytoma; sarcoma.

Figure 1

Solitary fibrous tumor involving the prostate with benign features. (A) Low power view with fascicular pattern and occasional large, sometimes branching blood vessels; (B) high power view showing oval to spindle-shaped nuclei and cells with focally fascicular pattern; (C) CD34 immunohistochemical stain with cytoplasmic staining; (D) STAT6 immunohistochemical staining with nuclear staining. H&E staining; A: ×100; B,C,D: ×200.

Figure 2

Solitary fibrous tumor of the pelvis of a male patient with malignant features. (A) Low power view with frequent, sometimes branching blood vessels; (B) high power view with nuclear enlargement and pleomorphism and coagulative tumor necrosis; (C) high power view showing overtly malignant nuclear features and frequent mitoses; (D) STAT6 immunohistochemical stain with nuclear staining. H&E staining; A: ×100; B,C,D: ×200.