In animal models, mutations in CTNNB1 (exon 3) are predominant events among mutations of multiple genes in colon tumors induced by 2-amino-1-methyl-6-phenylimidazo [4,5-b] pyridine (PhIP) and dextrin sulfate sodium (DSS) in humanized CYP1A mice, one type of mice possessing human CYP1A gene to replace mouse Cyp1a gene. This evidence concerns the gene CTNNB1 and colonic neoplasm.