Malignant transformation of oral leukoplakia: a retrospective cohort study of 218 Chinese patients.

Background: Oral leukoplakia (OL) is the best-known potentially malignant disorder. A new binary system to grade dysplasia was proposed by WHO, but the biological significance in predicting malignant transformation risk is unknown. The objective of this study is to estimate the rate of malignant transformation in a long-term follow-up cohort, explore the usefulness of the new binary system of grading dysplasia and identify significant risk factors of OL malignant transformation in China.

Methods: A total of 218 patients with clinical and histopathologic diagnosis of OL were retrospectively reviewed. They were selected among all archived files at the Department of Oral Mucosal Diseases, Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine. The mean follow-up period was 5.3 years.

Results: Among 218 cases, 39 (17.9%) OL patients developed oral cancer, with a mean duration of 5.2 years. Cox regression analysis revealed that dysplasia was an independent risk factor for OL malignant transformation, but age, gender, lesion site, diet habit, smoking and ethanol intake were not risk factors. High-risk dysplastic OL was associated with a 4.57-fold (95% confidence interval, 2.36-8.84; P < 0.001) increased risk of malignant transformation, compared with low-risk dysplasia. Consistent with this result, high-risk dysplastic OL had significantly higher malignant incidence than low-risk dysplasia, particularly during the first 2-3 years of follow-up, by Kaplan-Meier analysis (Log-rank test, P < 0.001).

Conclusions: The new binary system's function in predicting OL malignant transformation risk was investigated in this survey. The utilization of high-risk dysplasia as a significant indicator for evaluating malignant transformation risk in patients with OL was suggested, which may be helpful to guide treatment selection in clinical practice.