Objectives: To evaluate current evidence on the malignant transformation of oral lichen planus (OLP), oral lichenoid lesions (OLLs), and oral lichenoid reactions (LRs) and to determine the variables with greatest influence on cancer development.
Material and methods: We searched PubMed, Embase, Web of Science, and Scopus for studies published before November 2018. We evaluated the quality of studies (QUIPS tool). We carried out meta-analyses to fulfill our objectives. We examined the between-study heterogeneity and small-study effects, and conducted sensitivity studies and subgroup analyses.
Results: Inclusion criteria were met by 82 studies (26,742 patients. The combined malignant transformation rate was 1.14% for OLP (95% CI = 0.84-1.49), 1.88% for OLLs (95% CI = 0.15-4.95) and 1.71% for LRs (95% CI = 0.00-5.46). Subgroup analysis revealed a higher malignant transformation rate in studies when the presence of epithelial dysplasia was not an exclusion criterion (p = 0.001), when both clinical and histopathological criteria were used for diagnosis (p < 0.001), when the follow-up was at least 12 months (p = 0.048), and when there was lower risk of potential bias (p = 0.002). Malignant transformation risk factors were: tongue localization (RR = 1.82, 95% CI = 1.21-2.74, p = 0.004), presence of atrophic-erosive lesions (RR = 4.09, 95% CI = 2.40-6.98, p < 0.001), tobacco use (RR = 1.98, 95% CI = 1.28-3.05, p = 0.002), alcohol consumption (RR = 2.28, 95% CI = 1.14-4.56, p = 0.02), and hepatitis C virus infection (RR = 4.46, 95% CI = 0.98-20.22, p = 0.053).
Conclusions: The malignant transformation rates of OLP, OLLs and LRs are underestimated due essentially to restrictive diagnostic criteria, inadequate follow-up periods, and/or low quality of studies.
Keywords: Malignant transformation; Meta-analysis; Oral cancer; Oral lichen planus; Oral lichenoid lesions.
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