In spite of the fact that CEA and CEACAM6 are normally up-regulated as differentiation proceeds during the movement of colonocytes up colonic crypts [4], [8], experiments with various model systems in vitro, including cultured human colorectal carcinoma colonocytes, have shown that if CEA and/or CEACAM6 are inappropriately up-regulated in cells with division potential prior to differentiation, differentiation is blocked [9]–[11], cell polarization and tissue architecture are disrupted [10] and anoikis/apoptosis is inhibited [12]–[15]. The gene discussed is CEACAM5; the disease is colorectal carcinoma.