IMMUNOHISTOCHEMICAL DETECTION OF A DNA REPAIR GENE PRODUCT AND A CELL CYCLE REGULATOR IN ORAL LICHEN PLANUS

Abstract

There is a need for objective methods of assessment of oral epithelial precancerous lesions and reliable markers for the prediction of malignant change in these lesions. This study was thus conducted to examine the immunohistochemical expression of a cell cycle regulator; p16, and a DNA repair gene product; topoisomerase II α in OLP, as well as their relation to the clinical variants and the malignant potentiality of OLP. Thirty- nine cases of OLP were selected, and classified according to their clinical variants into 22 reticular and 17 atrophic cases, as well as to the histological presence of dysplastic criteria, into 19 non-dysplastic and 20 dysplastic cases. Using peroxidase-antiperoxidase method for immunohistochemical examination, each specimen was stained with either anti-p16 or anti-topo IIα antibodies. For result interpretation, a quantitative assessment of p16 and topo IIα antibody expression was carried out using the image analysis software (Image J, 1.41a, NIH, USA). Results of the present study revealed that 31 out of 39 OLP cases (79.5%), showed p16-immunopositivity in the epithelium, where as 15 out of 39 OLP cases (38.5%) expressed topo IIα immunopositivity. Statistical analysis of p16 revealed a significant statistical difference between the reticular and the atrophic variants of OLP (p = 0.01) reflecting the more significant role of p16 in the reticular than in the atrophic variants. This implies that p16 expression is more likely to be related to increased rate of cellular proliferation which in turn suggests that changes in the proliferative potential are an early effect on p16 expression. Topo IIα indices also showed a significant statistical difference between the reticular and the atrophic variants of OLP (p = 0.05) reflecting the more essential role for topo IIα in the reticular than in the atrophic variant. This implies that topo IIα is a better proliferation rather than apoptotic marker in OLP. On the other hand, neither p16 nor topo IIα showed any significant difference between dysplastic and non-dysplastic cases of OLP (p= 0.46 and 0.6 respectively). Thus, both markers were found to be not ultimate estimates for differentiating dysplastic from non-dysplastic mucosa in oral cavity biopsies.