PROLIFERATIVE ACTIVITY OF CALCIFYING ODONTOGENIC CYSTS AS EVALUATED BY PROLIFERATING CELL NUCLEAR ANTIGEN LABELING INDEX

The calcifying odontogenic cyst (COC) presents with diverse histologic al features; thus, several subclassifications have been proposed. To e valuate the significance of the various histological features and subt ypes of COC from the perspective of proliferative activity, the prolif erating cell nuclear antigen (PCNA) labeling index (LI; the percentage of positive nuclei) was assessed immunohistochemically in 25 cases of COC (21 benign and four malignant). All of the benign cases were of t he cystic variety and further subclassified into non-proliferative sub type (NPS; four cases); proliferative subtype (PS; eight cases); and C OC associated with odontoma (COCaO, nine cases). The PCNA LI of the ma lignant COC (65.2 +/- 5.6) was significantly higher than that of the b enign COC (11.6 +/- 9.0; P = 0.002). Non-proliferative subtype (6.8 +/ - 2.8) showed the lowest PCNA LI and PS (17.2 +/- 11.2) the highest of among the three subtypes of benign cystic COC (P = 0.028). In nine ca ses of COCaO, six showed epithelial lining of the non-proliferative ty pe as NPS and the other three had lining with proliferative features a s PS. The PCNA LI of the latter COCaO group (14.3 +/- 6.6) was signifi cantly higher than that of the former (6.1 +/- 4.3; P = 0.05), as seen between PS and NPS. These results demonstrate that PCNA LI is a possi ble parameter for differentiating malignant COC from benign COC and, w hatever the subtypes, the proliferative features in the lining are the main factor influencing the proliferating activity of COC.