The reported rates of transformation of oral lichen planus

Objectives: Our aim was to investigate the source, variability and robustness of oral lichen planus (OLP) malignant transformation rates quoted in the literature. Materials and methods: Online indexed scientific literature reporting the association of OLP with malignant transformation was searched yielding the largest analysis of such episodes to date (65 papers, accumulating 24097 cases of OLP, with 386 instances of subsequent malignancies) resulting in a raw integrated transformation rate of 1.60%. Results: The data spans 88 years but is poorly standardised. A "yearly rate of malignant transformation" was estimated in papers where either the average ( n= 32) or the range of follow up times ( n= 18) was reported. These ranged from 0% to 2.03% transformations/year (average 0.43%, median 0.25%/year). However, these rates appear to overestimate the malignant transformation frequencies of oral lichen planus when considering the overall incidence of oral cancer in the UK. Conclusion: While there was evidence of an association of OLP with risk of subsequent malignant transformation, a number of factors resulting from the lack of standardisation in the reports obscure the elucidation of the real risks associated with the disorder. We suggest the use of structured, standardised reporting to facilitate parsing and summarising future data.