A Molecular Hypothesis on Malignant Transformation of Oral Lichen Planus: A Systematic Review and Meta-Analysis of Cancer Hallmarks Expression in This Oral Potentially Malignant Disorder

Simple Summary Oral lichen planus (OLP) is a chronic inflammatory disease of autoimmune nature and unknown etiology which affects approximately 1% of the world's population. The most important feature of OLP is its behavior as an oral potentially malignant disorder (OPMD). The current study is the first systematic review and meta-analysis designed to evaluate the degree of existing scientific evidence on the cancer hallmarks proposed in 2011 by Hanahan and Weinberg, defined as the characteristics that cells must fulfill in order to be considered neoplastic cells in all types of tumors that affect humans. This systematic review and meta-analysis includes 110 studies which recruited 7064 cases of OLP, in which the expression of 104 molecular biomarkers were analyzed through an immunohistochemical technique. The earliest oncogenic molecular mechanisms that could justify the malignant transformation of this disease are analyzed in depth and critically discussed on the basis of evidence.Abstract We aimed to qualitatively and quantitatively analyze, through a systematic review and meta-analysis, the current evidence on the differential expression of the hallmarks of cancer in oral lichen planus (OLP) samples, in order to know the earliest molecular mechanisms that could be involved in the malignant transformation of this oral potentially malignant disorder. We searched MEDLINE/PubMed, Embase, Web of Science, and Scopus for studies published before November 2023. We evaluated the methodological quality of studies and carried out meta-analyses to fulfill our objectives. Inclusion criteria were met by 110 primary-level studies, with 7065 OLP samples, in which the expression of 104 biomarkers were analyzed through immunohistochemistry. Most OLP samples showed sustained cell proliferation signaling (65.48%, 95%CI = 51.87-78.02), anti-apoptotic pathways (55.93%, 95%CI = 35.99-75.0), genome instability (48.44%, 95%CI = 13.54-84.19), and tumor-promoting inflammation events (83.10%, 95%CI = 73.93-90.74). Concurrently, OLP samples also harbored tumor growth suppressor mechanisms (64.00%, 95%CI = 53.27-74.12). In conclusion, current evidence indicates that molecular mechanisms promoting hyperproliferative signaling, an antiapoptotic state with genomic instability, and an escape of epithelial cells from immune destruction, are developed in LP-affected oral mucosa. It is plausible that these events are due to the actions exerted by the chronic inflammatory infiltrate. Malignant transformation appears to be prevented by tumor suppressor genes, which showed consistent upregulation in OLP samples.