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Case Reports

Abstract

Solitary fibrous tumor (SFT) is an uncommon mesenchymal tumor classified as either typical or malignant, according to the 2020 World Health Organization (WHO) risk stratification. SFT generally presents as a well-defined mass, typically located in the abdominal cavity, limbs, and pleura. Exceptionally rare, only one case has been documented within the subungual region, and we report a second such occurrence, specifically in the nail bed.

The patient, a 64-year-old woman, has experienced abnormalities in her right ring finger's nail and nailbed for several years. She has a medical history of primary hyperaldosteronism but reports no trauma to the affected area. Clinical examination revealed nail ridging; the nail was thin, soft, and elevated due to an underlying mass, presumed to be either a cyst or a soft tissue tumor. Surgical excision was pursued. During the operation, the mass was observed as a yellow-white, well-circumscribed entity, measuring 9 mm in diameter. Microscopic examination identified it as a cytologically bland spindle cell tumor with scant mitotic activity. Immunohistochemical tests showed strong positivity for STAT6 and weak positivity for CD34, with negativity for desmin, SMA, factor XIIIa, S-100, and loss of RB1. Given the rarity of its location, next-generation sequencing was conducted, revealing a NAB2::STAT6 fusion, confirming the diagnosis of solitary fibrous tumor.

This case underscores the importance of considering SFT in differential diagnoses for unusual subungual lesions and highlights the utility of molecular diagnostics in confirming rare presentations.