Since human colonic tumorigenesis is in fact focal, we suggest that, unlike the situation here where every cell has multiple copies of CEA and CEACAM6 genes, their over-expression itself in the adult human colon could occur by focal up-regulation in expression as observed in the carcinogen-induced colon tumors in CEABAC2 and CEABAC10 mice [41]. This evidence concerns the gene CEACAM3 and colonic neoplasm.