CEACAM5 and colorectal cancer: In the control group, nude mice bearing CEA-positive tumors (LS174T colorectal cancer) received 111In-labeled anti-CEA antibody or 111In-labeled streptavidin were sacrificed at 5 h p.i. In the pretargeting group, the animals received unlabeled streptavidin followed by 111In-labeled biotin at 3 h later.