• Analysis indicates a reduced risk of cancer and a suggestion of a dose-dependent effect.• Speculate a link between the putative anti-cancer effect of metformin and its action to activate AMPK and role of the upstream serine-threonine kinase, LKB1, a known tumor-suppressor.• Conclusion: Epidemiological evidence that metformin reduces incidence of cancer. This evidence concerns the gene MARK2 and neoplasm.