Ossifying fibromyxoid tumor may express CD56 and CD99: a case report.

Ossifying fibromyxoid tumor (OFMT) is an uncommon soft tissue neoplasm characterized by a combination of myxoid and/or fibrous stroma with areas of ossification. Although most authors postulate a neuroectodermal origin for this peculiar tumor, there is no agreement in the literature regarding its histogenesis. In this article, we present the immunohistochemical findings of a case of a 39-year-old white male with an OFMT of the soft tissue in the mandibular region. The tumor was positive to S-100 protein, glial fibrillary acidic protein, CD99, CD56 and negative to smooth muscle actin, cytokeratins AE1/AE3, epithelial membrane antigen, and CD68. To the best of our knowledge, this is the first case reported to be positive to CD56 and CD99. Immunoreactivity to these two antibodies, together with reactivity for S-100 protein and glial fibrillary acidic protein, suggests that OFMT is of a neuroectodermal origin. In our opinion, in the absence of reactivity to at least one neuroectodermal marker one should seriously question a diagnosis of OFMT.