Oral dysbiosis in the onset and carcinogenesis of oral epithelial dysplasia: A systematic review

Objective: This systematic review aims to investigate possible connections between the oral microbiome and the onset and carcinogenesis of oral epithelial dysplasia (OED).Methods: A systematic search was performed on PubMed, Embase, Cochrane Database, and SCOPUS by two authors independently, addressing the focused question- "Has oral microbiome dysbiosis been involved in the onset and carcinogenesis of oral epithelial dysplasia?" We used the Newcastle-Ottawa scale to assess the quality of studies included in the review.Results: Out of 580 references screened, ten studies were found eligible for inclusion. All studies were case-control studies, and only qualitative analysis was conducted due to heterogeneous characteristics. The overall risk of bias in the eligible studies was considered as high. Microbiome diversity indices showed inconsistent evidence among studies. A significant increase of phylum Bacteroidetes in OED patients was reported in five studies. Five studies reported an increase of genus Fusobacterium in both the OED and oral squamous cell carcinoma (OSCC) patients and six different studies respectively reported a reduction of genus Streptococcus in both the OED and OSCC groups when compared to normal controls. Other predominant bacteria that were specific to different patient groups varied in each study.Conclusions: The results of the included studies showed that the composition of the oral microbiome in patients with OED compared to healthy controls and OSCC patients was inconsistent. However, all ten studies showed non-negligible heterogeneity in the type and size of the sample, and the comparability between groups, which strongly limited the external validity of results. Further studies are strongly recommended.