A comparative study of fibrous dysplasia and osteofibrous dysplasia with regard to expressions of c-fos and c-jun products and bone matrix proteins: A clinicopathologic review and immunohistochemical study of c-fos, c-jun, type I collagen, osteonectin, osteopontin, and osteocalcin

Fibrous dysplasia and osteofibrous dysplasia are both benign fibro-osseous lesions of the bone and are generally seen during childhood or adolescence. Histologically, the features of these bone lesions sometimes look quite si milar, but their precise nature remains controversial. We retrospectively s tudied clinicopathologic findings in 62 cases of fibrous dysplasia and 20 c ases of osteofibrous dysplasia with regard to their anatomic location and h istological appearance. From among these cases, the immunohistochemical exp ressions of c-fos and c-jun proto-oncogene products and bone matrix protein s: of type I collagen, osteonectin, osteopontin, and osteocalcin were evalu ated in 20 typical fibrous dysplasias and 17 osteofibrous dysplasias using paraffin sections, and these expressions were then assessed semiquantitativ ely. Microscopically, fibrous dysplasia showed various secondary changes, s uch as hyalinization, hemorrhage, xanthomatous reaction, and cystic change in 22 of the 62 cases (35%). This was a higher incidence than in osteofibro us dysplasia, in which only 2 of the 20 cases (10%) showed such changes. In the elderly fibrous dysplasia cases, the cellularity of fibroblast-like ce lls was rather low, and those cases were hyalinized. Almost all of the case s of fibrous dysplasia and osteofibrous dysplasia showed positive expressio ns of c-fos and c-jun products. The expressions of type I collagen and oste opontin showed no difference between fibrous dysplasia and osteofibrous dys plasia. Immunoreactivity for osteonectin in bone matrix was detected in onl y 1 case of fibrous dysplasia (1 of 20), whereas it was recognized in 14 of the 17 cases of osteofibrous dysplasia. Furthermore, the immunoreactivity for osteocalcin in bone matric and fibroblast-like cells was higher in fibr ous dysplasia than it was in osteofibrous dysplasia, semiquantitatively. Ou r immunohistochemical results regarding osteonectin and osteocalcin suggest that the bone matrix of fibrous dysplasia is somewhat more mature than tha t of osteofibrous dysplasia, and that the fibroblast-like cells in fibrous dysplasia share some phenotypic features with osteoprogenitor cells of norm al osteogenic tissues. Fibrous dysplasia and osteofibrous dysplasia share s ome similar histological features, including c-fos and c-jun expressions, a lthough different clinicohistologic features and immunohistochemical expres sions of osteonectin and osteocalcin were observed. These features suggest that the mechanisms behind the development of fibrous dysplasia and osteofi brous dysplasia are similar, but this is not necessarily indicative of a cl oser relationship between the 2 diseases. Copyright (C) 1999 by W.B. Saunde rs Company.