Intraoral Sclerotic Fibroma: A Detailed Immunohistochemical Study Highlighting Expression of Histiocytic Markers.

Sclerotic fibroma (SF), initially described as a cutaneous manifestation of Cowden syndrome (CS), is an uncommon, well-circumscribed tumor characterized by sclerotic, hyalinized collagen bundles. Originally considered a sclerotic variant of benign fibrous histiocytoma (BFH), most SFs express FXIIIA, and despite this, there is limited investigation of other histiocytic markers. Additionally, SF-like changes in BFH and other cutaneous lesions may create diagnostic pitfalls. Nonetheless, consistent expression of CD34 and CD99, in close histomorphological correlation, supports the diagnosis of SF. To date, approximately 11 intraoral SFs have been reported, none associated with CS. We present an immunohistochemical analysis of a typical SF in the buccal mucosa of a 46-year-old male without signs of CS. Immunohistochemistry showed positivity for vimentin, CD34, CD99, collagen IV (focal), and α-SMA (focal). Notably, CD68, CD163, FXIIIA, and lysozyme were also positive, suggesting a histiocytic population infiltrating the stroma. This case reinforces that histomorphology, along with CD34 and CD99 immunoprofile, is essential to distinguish SF from BFH and other sclerosing mesenchymal neoplasms. Furthermore, our findings raise the possibility that a subset of SFs may harbor a histiocytic component, which could contribute to its pathogenesis or reflect a reactive stromal component.