Solitary fibrous tumor of the oral cavity with a predominant leiomyomatous-like pattern: A potential diagnostic pitfall

The diagnosis of solitary fibrous tumor(SFT)is usually straightforward if the typical morphologicfeatures,including a wide variety of growth patterns,are identified. We report the clinical,radiologic,and pathologic findings of a rare case of intraoral SFT which exhibited a predominant leiomyomatous-like appearance,closely reminiscent of a leiomyoma,at both incisional and excisional biopsy.Histologically, the tumor was composed predominantly of intersecting fascicles of eosinophilic spindle-shaped cells, variably set in a fibrous stroma.A focal hemangiopericytoma-like growth pattern withalternating hypercellular and hypocellular areas, as well as the deposition of dense keloid-type collagen,raising the suspicion of SFT,could be identified only after a careful examination of the whole tumor.Immunohistochemistry was helpful in confirming the diagnosis of SFT,revealing a diffuse staining ofneoplastic cells for vimentin,CD34,bcl-2 protein,and,focally,CD99.Myogenic markers(alpha-smoothmuscle actin,desmin,h-caldesmon)were not expressed.The pathologist should be aware of this variant of intraoral leiomyomatous-like SFT to avoid amisdiagnosis of leiomyoma.The distinction of SFT from leiomyoma in the oral cavity is important toassure both correct treatment and prognostic information.