Malignant transformation of oral leukoplakia: a systematic review of observational studies

The aim of this systematic review was to ascertain the malignant transformation rate of oral leukoplakia and the associated risk factors.

Published literature was searched through several search engines from 1960 to the end of December 2013. The inclusion criteria included 'leukoplakia', 'pre-cancer', 'malignant transformation', 'follow-up' and 'outcome'. Two reviewers extracted the data independently and also assessed the quality of evidence.

The search strategy resulted in 1032 abstracts or full-text articles, of which 24 met the inclusion criteria. There was much variation in the definitions used by the various authors in their original reports to define oral leukoplakia or in the criteria used to recruit their patients for follow-up. The estimated overall (mean) malignant transformation rate for the total population described in these 24 studies amounts to 3.5% (405/11423), with a wide range between 0.13% and 34.0%. Based on the evidence presented, the features that stand out as significant determinants contributing to malignant potential of OL include advanced age, female sex, leukoplakia exceeding 200 mm(2) , non-homogeneous type (eg. erythroleukoplakia) and the higher grades of dysplasia.

The review indicates that drawing meaningful evidence-based conclusions are difficult from retrospective studies of this nature. However, many of the determinants exposed in the review require further investigation by well-designed prospective studies.