Abstract
Data sources Four electronic databases (PubMed, Web of Science, Scopus and PLOS) were queried to identify studies that investigated the effects of probiotics against oral cancer, published in the English language between January 2015 and February 2020.Study selection Randomised controlled trials (RCT) including in vivo and in vitro studies that evaluated the effects of probiotics against oral cancer were included.Data extraction and synthesis The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA-P) 2015 guidelines were followed to conduct this systematic review. Screening of titles, abstracts and full texts was done independently by four authors with disagreements resolved by mutual discussion. Individual studies' year, author, country, as well as strain of probiotics, type of sample, mechanisms of probiotics and outcomes, were analysed by two authors. The methodological quality of the included studies was assessed using the Joanna Briggs Institute (JBI) Critical Appraisal Tools (Checklist for Randomised Controlled Trial) by three authors. Meta-analysis was performed with Review Manager software, Version 5.3 and results were reported in odds ratio. Inconsistency test (I2) was used to examine the heterogeneity between studies.Results From an initial 774 articles, only five met the study eligibility criteria to be included in this review. Two studies used in vivo animal models and three studies conducted in vitro experiments using cancer and normal cell lines. There were no studies on humans. Four probiotics were reported to inhibit oral carcinogenesis; namely, Acetobacter syzygii (A. syzygii), Lactobacillus plantarum (L. plantarum), Lactobacillus salivarius (L. salivarius) Ren and AJ2 (combination of Streptococcus thermophiles, Bifidobacterium breve, Bifidobacterium longum, Bifidobacterium infantis, Lactobacillus acidophilus, Lactobacillus plantarum, Lactobacillus casei, Lactobacillus bulgaricus). Two studies that used L. salivarius Ren were combined quantitatively in a meta-analysis which showed 95% reduction of risk in oral cancer development (OR = 0.05, 95% CI 0.01-0.23; p <0.05).Conclusions Within the limitations of in vivo (animal) and in vitro (cell lines) studies, the authors concluded that the probiotics analysed in this review, especially L. salivarius Ren, seem to play a role in oral cancer inhibition.
