Carcinoembryonic antigen (CEA) in human colorectal cancers growing subcutaneously in nude mice

Eleven human colorectal xenografts from 26 tumor lines established in nude mice in our laboratory were investigated for carcinoembryonic antigen (CEA) production. Serum levels of CEA in nude mice were markedly elevated in all cases but one, median values ranging from 3.7 to 42.8 ng/ml. Carcinoembryonic-antigen levels for ten nontumor-bearing nude mice ranged from 0.00 to 0.12 ng/ml (median value 0.07). A clear linear correlation could be demonstrated between log CEA serum levels and log tumor volumes in serial measurements. In one case, CEA was normal in the cancer patient's serum and gave the lowest value (3.7 ng/ml) in nude mice bearing the xenograft. By the indirect peroxidase technique, CEA was localized mainly on the apical cell membranes of the cancerous glands and in necrotic areas; only small amounts were detectable in the cytoplasm. Transplantation of human colorectal carcinomas into nude mice offers an excellent experimental in vivo system to study the mechanism of release, metabolism, and excretion of the marker.