Immunohistochemical profile of peripheral ameloblastomas

OBJECTIVE: Peripheral ameloblastoma (E/PA) is a rare variant of ameloblastoma occurring in the extraosseous region. Whereas the intraosseous ameloblastoma (IA) is a locally aggressive neoplasm capable of invasive behavior and destruction of bone, the E/PA does not manifest such behavior. In the present study, we examined the immunohistochemical localization of podoplanin, E-cadherin, vimentin and heparanase in E/PA, and based on our findings discuss the biologic behavior of the tumor. METHODS: Three cases of E/PA were retrieved from the pathology files of 100 cases of ameloblastoma that had been registered at our hospital. Immunohistochemical staining was performed using a monoclonal antibody for podoplanin, and polyclonal antibodies for E-cadherin, vimentin and heparanase. RESULTS: All cases of E/PA expressed podoplanin and heparanase in peripheral columnar cells and in the transitional zones between morphologically normal and altered epithelium. The staining was quite distinctive and unique, similar to our previously reported finding for IA. Vimentin was positive in stromal cells near tumor nests in all cases, and negative in epithelial tumor cells. E-cadherin showed weak reaction in tumor cells, the strongest reaction was found in stellate reticulum-like cells and acanthomatous areas; also enhanced expression was found in areas of continuity between the oral mucosa and the tumor nests. CONCLUSION: The localization of podoplanin and heparanase was similar to those in IA, but different in intensity; recurrence or bone involvement have not been found in any cases until now, supporting the possible role of the molecules in the process of invasion. Vimentin and E-cadherin were similar in IA and E/PA. The low expression of podoplanin and heparanase in E/PA compare to their expression in IA suggests that these molecules are related to the clinical behavior of the tumors, and will be good prognostic indicators.