Background : Osteopontin (OPN) is a glycoprotein involved in inflammation, angiogenesis, and cancer metastasis, and has been found in the epithelium of keratocystic odontogenic tumor (KCOT) recently.

Objective : Marsupialization and decompression is a frequently performed operation as a conservative therapy for large keratocystic odontogenic tumour. In this study, we observed the changes in OPN expression in the KCOT epithelium before and after decompression.

Methods : Sixteen pairs of paraffin-embedded tissue specimens obtained at the time of decompression and secondary curettage or enucleation were collected and immunohistochemically examined using antibody against OPN. The intensity of OPN staining was evaluated with a semi-quantitative detection method and the data statistically analysed.

Results : Immunohistochemical reactivity for OPN was consistently strongly to mildly positive in 90% of KCOT epithelium in samples before decompression. The positive staining was just localised to the cell membrane in the cuticular layer. But negative results were gained in all samples from the secondary curettage. The expression level of OPN was significantly decreased after decompression ( p < 0.05).

Conclusion : Significant loss or reduction of OPN expression was observed in KCOT epithelium after the decompression. OPN may be related to the local invasion and bone destruction of KCOT.