Changes in serum and tissue carcinoembryonic antigen with growth of human gastric cancer xenografts in nude mice

Four human gastric cancer xenografts in nude mice were analyzed for tumor growth and associated levels of carcinoembryonic antigen (CEA) in sera and tissues. The xenografts were established from gastric cancer patients and transplanted serially over 20 passages in our laboratory. Histologically, two xenografts were intestinal type and the other two were diffuse type. All of them were positive for CEA immunohistochemically. Individual xenografts showed a positive correlation between tumor growth and serum CEA level, with correlation coefficients ranging from 0.73 to 0.91. Serum CEA levels rose continuously with increasing tumor weight after inoculation. A positive correlation was also observed between the tissue CEA level and tumor growth, the former increasing along with the latter, showing the correlation coefficients ranging from 0.69 to 0.81. Furthermore, the level of serum CEA closely paralleled to that of tissue CEA, showing the correlation coefficients ranged 0.54 to 0.90. The deviation of the ratio of serum CEA level/tissue CEA level was constant among the xenografts, although the mean ratio differed slightly. These results suggest that serum CEA level is closely correlated with tissue CEA level as well as tumor growth, and that the elevation of serum CEA is attributable to the tissue CEA level rather than tumor weight.