Superficial solitary fibrous tumor masquerading as a dermoid cyst: a case report.

Abstract

Solitary fibrous tumors (SFTs) are relatively rare spindle cell neoplasms uncommonly seen in dermatology practice. Initially discovered as a pleural tumor, SFTs have also been found in extra-pleural sites including the skin and soft tissues. When arising within the dermis or subcutis they are termed superficial SFTs, where they often present as solitary, unilateral, slow growing superficial masses. Histologically, they are composed of spindle cells arranged in a "patternless" pattern with hemangiopericytoma-like vessels dispersed throughout. Historically, CD34, CD99 and Bcl-2 immunohistochemical (IHC) stains were used to differentiate SFTs from other spindle cell neoplasms, however these markers are not entirely specific. Recent discovery of a disease defining NGFI-A binding protein 2 (NAB2)-signal transducer and activator of transcription 6 (STAT6) fusion gene has led to the use of STAT6 IHC staining to help verify the diagnosis of SFTs, particularly in unexpected sites. We report a case of a 23-year-old woman with a slowly growing lateral supra-orbital mass, clinically concerning for a dermoid cyst, which was subsequently discovered to be a SFT on pathologic examination, with the diagnosis being verified by STAT6 immunostaining. SFTs are rarely encountered in dermatologic practice, however, must be kept on the differential of subcutaneous nodules, including those occurring in young adults. Due to the rarity of these tumors in clinical practice, a proposed algorithm for the approach to management of SFTs is included, guided by a validated, histology-driven, metastatic risk assessment tool, to help guide other clinicians confronted by these tumors.