CEACAM5 and colorectal cancer: Since, as in humans, CEACAM7 is expressed only at very low levels in these transgenics' colons [30] and is under-expressed rather than over-expressed in human colorectal cancers [1], and CEACAM3 is not at all expressed in the colon [1], [30], it seems very likely that CEA and/or CEACAM6 are responsible and, in fact, both of the latter genes have been shown to elicit tumorigenic effects in various model systems in vitro and in xenograft mouse models [9]–[15], [40].