RANK, RANKL, and OPG in recurrent solid/multicystic ameloblastoma: their distribution patterns and biologic significance.

OBJECTIVES: To determine the distribution patterns of bone resorption regulators, receptor activator of nuclear factor kappa-B (RANK), RANK ligand (RANKL), and osteoprotegerin (OPG) in recurrent ameloblastoma (RAs) and to clarify their impact on the biologic behavior of these neoplasms. MATERIALS AND METHODS: Fifteen paraffin-embedded RA cases were subjected to immunohistochemistry for expression of RANK, RANKL, and OPG. RESULTS: The RANK-RANKL-OPG triad was heterogeneously detected in RA samples. RANK, essential for osteoclast differentiation, was strongly expressed in tumoral epithelium. Conversely, RANKL, an osteoclast activator, was markedly underexpressed, and protein localization was predominantly stromal. OPG, an osteoclastogenesis inhibitory factor, was detected in neoplastic epithelium more than in stroma, suggesting functional inactivation of RANKL. Most RA (n = 12/15; 80%) exhibited a bimolecular spatial expression pattern, the most common being RANK-positive/OPG-positive (n = 8/15; 53.3%). All three proteins showed no significant correlation with the clinical/histopathologic parameters in RA patients (P > .05). CONCLUSIONS: The RANK(+)/RANKL(low/-)/OPG(+) phenotype observed in RA suggests an altered local bone metabolism characterized by low bone resorptive activity in these recurrent tumors.