Using CEA-producing human colonic adenocarcinoma cells (CX-1) grown as tumor xenografts that were subcutaneously implanted on the flank in Swiss nude mice, they demonstrated the feasibility of gamma probe detection of 131I-labeled anti-CEA polyclonal baboon antibodies within such subcutaneous implants and demonstrated the greater sensitivity of the gamma detection probe as compared to gamma camera imaging for small tumor implants [289,290]. This evidence concerns the gene CEACAM5 and colon adenocarcinoma.