Prognostic Implications of DNA Repair, Ploidy and Telomerase in the Malignant Transformation Risk Assessment of Leukoplakia

Abstract

Background:Although leukoplakia shows a higher risk for malignant transformation to oral cancer, currently there are no clinically relevant biomarker which can predict the potentially high risk leukoplakia. This study aimed to investigate the genetic alterations such as DNA ploidy, telomerase expression and DNA repair capacity as predictive markers of malignant transformation risk of leukoplakia. Methods:The study was initiated in September 2005 and patients were followed up to March 2014. Two hundred patients with oral leukoplakia, 100 patients with oral cancer and 100 healthy, age and sex matched adults with normal oral mucosa as controls were recruited. The DNA ploidy content was measured by high resolution flow cytometry, level of telomerase expression was identified by TRAP assay and intrinsic DNA repair capacity was measured by mutagen induced chromosome sensitivity assay of cultured peripheral blood lymphocytes. The Chi-square test or Fisher’s Exact test was used for comparison of categorical variables between biomarkers. A p value less than or equal to 0.05 was considered as statistically significant. Analysis was performed with SPSS software version 16. Logistic regression was used to find the association between the dependent and three independent variables. Results:There was significant difference in the distribution of ploidy status, telomerase activity and DNA repair capacity among control, leukoplakia and oral cancer group (p<0.001). When the molecular markers were compared with histological grading of leukoplakia, both DNA ploidy analysis and telomerase activity showed statistical significance (p<0.001). Both aneuploidy and telomerase positivity was found to coincide with high-risk sites of leukoplakia and were statistically significant (p<0.002 and 0.02). All the leukoplakia and oral cancer patients were followed up for 8.5 years. Out of 200 cases of leukoplakia, 19 were found to be malignancy at the time of diagnosis. So for the calculation of risk of malignant transformation only 181 cases of leukoplakia were considered. Out of this 181 cases of leukoplakia, 12 (6.6%) underwent malignant transformation over a period ranging from 6 to 36 months. Univariate analysis showed DNA repair capacity and DNA ploidy as markers having significant risk association whereas multivariate analysis showed DNA repair capacity as the most significant marker to assess malignant transformation risk of leukoplakia (OR 52.9, 95% CI, 6.56 – 426.7). Conclusion:Genomic markers combined with clinical and histopathological evaluation can help identify the potentially high risk leukoplakia which can then be treated based on an individual approach.