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Case Reports

Abstract

Solitary fibrous tumor (SFT) is a rare fibroblastic mesenchymal tumor that accounts for less than 2% of all soft tissue tumors. It is now recognized that SFT is consistently associated with NAB2::STAT6 fusion, and is a major cause of its pathogenesis. It was first described in 1931 as a distinct tumor arising from the pleura.  SFTs can be found in any part of the body. Clinically, it is a slow-growing, painless, well-circumscribed mass, and its size is usually 5-10 cm in diameter. Generally, it can be successfully treated by complete excision to obtain tumor negative margins. There is a proposed risk stratification for SFT metastasis. Herein, we present a 73-year-old female who presented with a soft tissue lump on the right side of her scalp which has been slowly increasing in size over the past 10-15 years. It became significantly larger over the previous 3-4 years. Due to the level of discomfort affecting her daily life, a clinical decision to excise the mass was made. Histologic examination of the excised mass showed a subcutaneous well-circumscribed encapsulated neoplasm with variable cellularity randomly arranged, with associated branching vessels, perivascular hyalinization, and stromal myxoid changes. Immunohistochemical stains were performed, and it revealed that the neoplastic cells were diffusely and strongly positive for CD34 and STAT6, supporting the diagnosis of SFT. This lesion was classified as low-risk for metastasis per proposed risk stratification. Most of the reported superficial SFTs are classified as low-risk and behave in an indolent manner.