Carcinoembryonic antigen in experimental rat gastrointestinal carcinoma

Detection of gastric carcinoma in the experimental rat can be difficult. We investigated whether or not serological testing for carcinoembryonic antigen might aid in the diagnostic process. Twenty-five young adult male Wistar rats were studied; 15 were treated with the carcinogen N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), and 10 received no treatment. A complete autopsy was done on the 22 animals (12 in MNNG group, 10 in control group) that completed the 37-week study. Serum obtained at autopsy was evaluated by radioimmunoassay for the presence of CEA-like immunoreactivity. Grossly normal stomach, as well as gastric and small bowel cancers, were also stained for CEA. Of the 12 autopsied animals in the MNNG group, eight had a total of 12 cancers (seven gastric and five proximal small bowel); in no animal was an elevated serum CEA level detected. Immunoreactive tissue CEA was demonstrable in normal stomach and in gastrointestinal cancers; the tumors usually stained less intensely than adjacent normal stomach and did not exhibit normal intracellular CEA distribution.