Regarding the association between the CYP3A4*1B and CYP3A5*1 alleles, the proportion of individuals carrying both variants is much higher for all the study groups (6.7%, 6.1% and 4.6% for liver, gastric or colorectal cancer patients and 7.4% for control subjects) than expected from a random association of these alleles (0.3 to 0.8% of individuals, as calculated from actual allele frequencies in the study groups). This evidence concerns the gene CYP3A4 and colorectal cancer.