Dedifferentiated adamantinoma with revertant mesenchymal phenotype.

In adamantinoma of long bones, an osteofibrous dysplasia-like form with scattered epithelial elements and a classic form with abundant epithelium are distinguished. Osteofibrous dysplasia-like adamantinomas occur in children and adolescents and behave relatively benign, whereas classic adamantinomas predominate in adults and have a more aggressive clinical course. Because some osteofibrous dysplasia-like tumors have progressed to classic adamantinomas, it is hypothesized that the former is a potential precursor of the latter, showing mesenchymal-to-epithelial transformation.