Immunohistochemical characterization of the keratocystic odontogenic tumor

Objectives: Keratocystic odontogenic tumor (KCOT) shows potential aggressivity and a marked tendency to recur, to some extent because of the presence of daughter cysts. However, the lining epithelium of the cysts has not been biologically characterized. In the present study, we examined immunohistchemically apoptosis, proliferative activity, and localization of bcl-2, cytokeratins (CK) 10, 13, 17, and 19 in KCOT to elucidate the reasons for the aggressive features and tendency to recur. Methods: Fourteen KCOTs and 15 ortho-odontogenic keratocysts (OOC) as controls were obtained from Osaka Dental University Hospital. Formalin-fixed, paraffin-embedded sections from biopsy and operative specimens were mounted on silane-coated glass slides. The sections were deparaffinized and autoclaved at 121℃ for 15 min in 10 mM EDTA solution (pH6.0) for antigen retrieval, and endogenous peroxidase activity was then blocked with 3% H₂O₂ solution. The sections were incubated with anti-CK 10, 13, 17, and 19, anti-bcl-2 oncoprotein, and anti-Ki-67 monoclonal antibodies each for 1 hr at room temperature (RT). After reaction with these monoclonal antibodies, the sections were treated with EnVision+ for 30 min at RT, visualized by 3, 3'-diaminobenzidine, and observed by light microscopy. Results: bcl-2 reactivity was much more strongly expressed in the basal cell layer of the lining epithelium of KCOT than in that of OOC. CK10 was localized in the keratinized and upper prickle cell layers of OOC and KCOT. CK13, 17, and 19 were detected in the keratinized and prickle cell layers of KCOT much more abundantly than in those of OOC. Ki-67 positivity was detected at higher frequency in the parabasal cells of KCOT than in those of OOC. Conclusion: Since bcl-2 inhibits apoptosis, the tendency of KCOT to recur might depend on the inhibition of apoptosis of the lining epithelial cells.