Adenomatoid odontogenic tumor: evidence for a mixed odontogenic tumor

Objective Adenomatoid odontogenic tumor (AOT) was classified by WHO as a mixed odontogenic tumor in 1992 and reclassified as an epithelial-only tumor in 2005 without clear rationale. The purpose of this study was to investigate if there was any evidence to suggest AOT might be a mixed odontogenic tumor. Study Design Immunohistochemical studies with nestin, dentin sialophosphoprotein (DSPP), cytokeratin, and vimentin were performed using 21 cases of AOT and the staining results were analyzed according to the various morphologic patterns seen in AOT. Sirius red stain was used to detect presence of collagen types I and III in AOT products. Results Our results showed that 20/21 (95.23%), 0/21 (0%), 21/21 (100%), and 20/21 (95.23%) cases expressed nestin, DSPP, cytokeratin, and vimentin, respectively. Some cells in rosette/duct-like structures (RDS) expressed nestin, vimentin or both, without cytokeratin. Co-expression of vimentin and cytokeratin, or nestin, cytokeratin, and vimentin were noted in some cells. Sirius red was positive in eosinophilic products in RDS, double-layered spheres and dentinoid. Conclusion Although most AOT cells appear epithelial, there is a small population of cells expressing mesenchymal proteins and secreting collagen types I and III. These evidence suggests that AOT is a mixed odontogenic tumor.