Adding Mendelian randomization to a meta-analysis-a burgeoning opportunity

Current literature is teeming with tens of thousands of meta-analyses, but only a small fraction made seminal contributions to enriching our understanding of the mechanisms of carcinogenesis, possibly due to chance, bias, confounding, or reverse causality. The incorporation of Mendelian randomization (MR) with a meta-analysis has revolutionized traditional practice and is emerging as a viable technique to strengthen causal unconfounded inferences from observational data. We therefore highlight the importance of integrated MR meta-analysis in cancer epidemiology and provide an overview of three existing instrumental selection strategies in medical literature.