Sporadic sclerotic fibroma of the oral soft tissues.

Sclerotic fibroma (SF) is an uncommon, benign fibrous neoplasm that may present either as a sporadic, small, solitary cutaneous mass, in otherwise healthy individuals, or as solitary or multiple, discrete skin nodules in patients with Cowden syndrome. Oral SF has been reported in patients with Cowden syndrome; however we now report the first documented series of sporadic SF originating within the oral mucosa. We describe 5 cases of SF arising in 3 women and 2 men with an age range of 43 to 66 years. The buccal mucosa was the site of involvement in 4 patients and the lower lip in 1 patient. Microscopically, each of the tumors was characterized by an unencapsulated, well-circumscribed, hypocellular submucosal nodule that was sharply demarcated from the surrounding tissues. The neoplasms were primarily composed of thick collagen bundles that were occasionally arranged in a storiform pattern. Prominent clefts separated many of the collagen bundles. In all cases, spindle and stellate-shaped cells containing fusiform or stellate-shaped nuclei and inconspicuous nucleoli were found scattered throughout the lesion. Occasional stellate-shaped, multinucleated cells were also seen. Many of the cells also exhibited long dendritic cytoplasmic processes. The tumor cells strongly expressed CD34 and vimentin, and occasionally factor XIIIa, but were negative for markers of myofibroblastic, neural or melanocytic differentiation. These findings confirm that oral SF represents a unique entity and should be differentiated from more commonly occurring benign fibrous lesions of the oral soft tissues.