Hallmarks of Cancer Expression in Oral Leukoplakia: A Scoping Review of Systematic Reviews and Meta-Analyses

Background/Objectives: Oral leukoplakia (OL) is a prevalent oral potentially malignant disorder. Despite its clinical relevance, the molecular basis of its progression to malignancy is not yet fully elucidated. This scoping review of systematic reviews and meta-analyses aimed to synthesize current knowledge and evidence gaps regarding the implications of hallmarks of cancer expression in OL malignant transformation. Methods: A systematic search was conducted in MEDLINE, Embase, DARE, and the Cochrane Library to identify systematic reviews (with or without meta-analysis) published up to April-2025. Results: Twenty-two systematic reviews were included. The most frequently explored hallmark was activation of invasion and metastasis (n = 12; 32.40%), followed by tumor-promoting inflammation (n = 10; 27.03%), evasion of growth suppressors (n = 8; 21.60%), sustained proliferative signaling (n = 3; 8.10%), energy metabolism reprogramming (n = 2; 5.40%), replicative immortality (n = 1; 2.70%), and resistance to cell death (n = 1; 2.70%). No evidence was found for angiogenesis or immune evasion in OL. Conclusions: Available evidence indicates that OL may develop oncogenic mechanisms in early stages of oral oncogenesis, especially those related to sustained proliferation, evasion of growth suppressor signals, and cellular migration and invasion. Chronic inflammation also may facilitate the acquisition of other hallmarks throughout the multistep process of oral carcinogenesis. These findings also reveal evidence gaps in underexplored hallmarks of cancer, which highlights the need to expand future primary- and secondary-level investigations to better define the molecular mechanisms underlying OL malignant transformation.