Search strategy
We systematically searched the PubMed, Embase, China National Knowledge Infrastructure (CNKI), and Wan Fang databases (up to Sep 12, 2020) by using the following strategy: (‘CYP1A1 OR ‘Cytochrome P450 1A1’) AND (‘polymorphism’ OR ‘variant’ OR ‘variation’ OR ‘mutation’ OR ‘SNP’ OR ‘genome-wide association study’ OR ‘genetic association study’ OR ‘genotype’ OR ‘allele’) AND (‘colorectal’ OR ‘colon’ OR ‘rectal’). The language was not limited in this study. In addition, the reference lists was checked if the publications were relevant review and meta-analyses studies.