Squamous odontogenic tumor: immunohistochemical identification of keratins

Two cases of squamous odontogenic tumors are described in terms of histopathology and keratin immunohistochemistry. Histopathologically, the lesions were composed of squamous epithelial islands without peripheral columnar cells and well-differentiated stromal tissue. Immunohistochemical detection of keratin proteins was done with the use of polyclonal antikeratin antiserum (TK, detecting 41 to 65 kDa keratins) and monoclonal antibodies (KL1, 55 to 57 kDa; PKK1, 40, 45, and 52.5 kDa). Staining for PKK1-detectable keratin was absent in tumor epithelial cells and that with KL1 and TK immunoreagents was confined to squamous cells, being strong in the keratinized cells. In view of the results, the squamous odontogenic tumor appears to arise from the rests of Malassez in periodontal tissue rather than from oral squamous epithelium.