Solitary Fibrous Tumor of the Vulva: Case Report of a Rare Entity and Review of Literature.

Solitary fibrous tumor (SFT) is an uncommon mesenchymal tumor of fibroblastic origin, which shows a prominent hemangiopericytoma-like branching pattern. It may be found at any location and can rarely involve the female genital tract with the vulva being the most common site of involvement. This is a case report of vulvar SFT in a 47-yr-old female who presented with a slow growing vulvar mass for 3 yr. Histologic examination showed a neoplasm composed of ovoid to spindle shaped cells with hypocellular and hypercellular areas in a collagenous background. Prominent hemangiopericytoma-like vessels were identified. Immunohistochemistry showed positive staining of the tumor cells for CD34, STAT6, ER, PR, and vimentin. Immunoshistochemical staining for desmin, SMA, and S100 was negative. The majority of SFTs have a NAB2-STAT6 gene fusion on chromosome 12, resulting in nuclear STAT6 overexpression, which is a sensitive and specific immunohistochemical marker for its diagnosis. Only 25 cases of vulvar SFT have been reported in the English literature and it should be considered in the differential diagnosis of spindle cell lesions at this site.