Nodular fasciitis and solitary fibrous tumor of the oral region: tumors of fibroblast heterogeneity

OBJECTIVE: Fibroblastic proliferations of the oral cavity are extremely varied, yet they share certain features-spindle cell morphology, collagen synthesis, and fasciculation. Nodular fasciitis is a cellular fibroblastic lesion, uncommonly located in the oral submucosa, that shows smooth muscle actin (SMA) immunoreactivity. Solitary fibrous tumor expresses a CD34 fibroblast phenotype. The aim of this study is to report instances of nodular fasciitis and solitary fibrous tumor in the orofacial region and investigate immunohistochemical markers to compare and contrast fibroblastic phenotypic heterogeneity in these tumors. STUDY DESIGN: Seven benign cellular fibrogenic tumors initially diagnosed as nodular fasciitis over a 10-year period were examined. Immunohistochemical markers, including S-100 protein, SMA, CD68, CD34, and vimentin, were used to further characterize these lesions. RESULTS: All tumors occurred in adults, and the buccal mucosa was found to be the favored site. The spindle cells in these tumors showed phenotypic heterogeneity both within and between tumors. All were vimentin-reactive and harbored small populations of CD68-positive macrophage/dendrocytes. Five tumors were SMA-positive and CD34-negative; the tumor in one case was SMA-negative and CD34-positive, and that in another was SMA-positive and CD34-positive. CONCLUSION: Although rare, nodular fasciitis and solitary fibrous tumor arise in oral submucosa, usually in the cheek. The histopathologic features and immunomarkers indicative of myofibroblastic differentiation are seen in nodular fasciitis, whereas solitary fibrous tumor is CD34-positive; however, one instance was found to be positive for both markers. All of these cases harbored subpopulations of CD68-positive cells. Immunomarkers are a valuable adjunct in differentiating nodular fasciitis from solitary fibrous tumor, yet some tumors may harbor heterogeneous fibroblast phenotypes.