Fibromatosis of the head and neck: morphological, immunohistochemical and clinical features.

The term fibromatosis indicates a proliferation of well-differentiated fibroblasts and myofibroblasts that develops in the soft tissue. This tumor has been considered locally aggressive because of the infiltrative growth pattern, but does not metastasize. Its occurrence in the head and neck region is not common, and very sporadically it may occur in the oral cavity or jaw bones. Two cases of adult fibromatosis are described here; one involving the submucosa of the middle hard palate and the other the subcutaneous area of the frontal bone. Tumor growth was rapid and bone involvement occurred in one case. Biopsies were taken and in both cases histological examination showed a tumor consisting of fibroblasts within a collagenous stroma, with rare atypia and mitoses. The patients underwent surgical resection with wide surgical margins; excised material was analyzed microscopically and a diagnosis of fibromatosis was rendered. Immunohistochemistry was positive for actin, vimentin and desmin, and negative for S-100, CD34, the progesterone receptors (PR)-A and PR-B and the estrogen receptors (ER)alpha and ERbeta. Follow-up at 5 years after surgery found both patients to be progression free. The clinical, histological and immunohistochemical features were analyzed to better characterize this form of the disease, that very rarely involves the oral cavity.