IMMUNOHISTOCHEMICAL DETECTION OF C-FOS AND C-JUN EXPRESSION IN OSSEOUS AND CARTILAGINOUS TUMORS OF THE SKELETON

The products of c-fos and c-jun proto-oncogenes form the heterodimeric complex AP-1 (activator protein 1), which play an important part in t he control of bone cell proliferation and differentiation and in the d evelopment of bone tumours. We examined the expression of c-fos and c- jun in a series of 52 primary skeletal neoplasms, using an immunohisto chemical method on formalin-fixed, paraffin-embedded sections. The exp ression of c-fos and c-jun was restricted to bone-forming lesions, whi le cartilaginous tumours were devoid of immunoreactivity. In benign os teoblastic lesions moderate c-fos and c-jun expression was found in 2 cases (18.1%). The highest levels of c-fos and c-jun expression were d etected in high-grade central osteosarcomas (7 of 15 cases with modera te/diffuse expression) while I telangiectatic osteosarcoma, 2 low-grad e central osteosarcomas, 1 low-grade periosteal osteosarcoma and 7 low -grade parosteal osteosarcomas were either negative or had low express ion. The high-grade component of a dedifferentiated parosteal osteosar coma showed diffuse immunoreactivity for both oncoproteins. Comparison of c-fos and c-jun expression by histological grade showed that high- grade osteosarcomas had a significantly higher expression of both onco proteins than did low-grade osteosarcomas (P = 0.01, Fisher's exact te st). Thus, c-fos and c-jun overexpression may be implicated in the dev elopment of high-grade osteosarcomas, but they appear to have little o r no relevance for the development of low-grade osteosarcomas and cart ilaginous skeletal neoplasms.