Malignant epithelial odontogenic tumors.

Malignant epithelial odontogenic tumors are very rare. They may arise from the epithelial components of the odontogenic apparatus. The rests of Malassez, the reduced enamel epithelium surrounding the crown of an impacted tooth, the rests of Serres in the gingiva, and the linings of odontogenic cysts represent the precursor cells for malignant transformation. Because metastatic carcinoma is the most common malignancy of the jaws, the diagnosis of a primary intraosseous carcinoma must always be made to the exclusion of metastatic disease. Odontogenic carcinomas include malignant (metastasizing) ameloblastoma, ameloblastic carcinoma, primary intraosseous squamous cell carcinoma, clear cell odontogenic carcinoma, and malignant epithelial ghost cell tumor. There are specific histopathologic features that support the diagnosis of a primary carcinoma of odontogenic epithelium which are presented in this article. Immunohistochemical (IHC) staining is important for distinguishing clear cell odontogenic carcinoma from metastatic renal cell tumors, yet IHC stains are not particularly helpful for other lesions in this group-all of which exhibit low molecular weight cytokeratin positivity. Aggressive growth and nodal and distant metastases occur with all of these entities.