Micrornas and their role in the malignant transformation of oral leukoplakia: A scoping review

Background: MiRNAs are small non-coding RNAs that regulate gene expression at the post-transcriptional level and have been associated with malignant transformation of oral epithelial precursor lesions such as oral leukoplakia. The aim was to perform a scoping review of the contemporary literature about the different roles of miRNAs during the malignant transformation of oral leukoplakia. Material and Methods: We conducted a systematic search with the following MeSH terms: ‘oral leukoplakia’, ‘carcinoma in situ’, ‘microRNAs’, ‘mouth neoplasms’ and ‘epithelial–mesenchymal transition’ in PubMed/MEDLINE, EMBASE and SpringerLink. Results: Fifteen articles were included for analysis, among which in vivo and in vitro articles were included. A total of 21 different miRNAs were found to be involved in the malignant transformation process of oral leukoplakia. Regarding their possible effects, 6 miRNAs were classified as oncogenic, 5 as tumour suppressors and 10 were related to epithelial–mesenchymal transition, invasion and migration. Conclusions: Based on the current review, we concluded that miRNAs-21, 345, 181-b and 31* seem to be potential markers of malignant transformation of oral leukoplakia. However, further clinical prospective studies are needed in order to validate their utility as prognostic biomarkers.