Inclusion and exclusion criteria
The inclusion criteria were as follows: (1) case–control or cohort studies, (2) explored the correlation between the CYP1A1 T3801C and A2455G polymorphisms and CRC risk, and (3) gave the genotype data of cases and controls or the odds ratio (OR) with their 95% confidence intervals (CI). Exclusion criteria were as follows: (1) review articles, (2) case reports, (3) editorials, (4) systematic review and meta-analyses, (5) other SNP, (6) other disease, (7) animal studies, and (8) duplicate data.