Further investigations of immunoreactive carcinoembryonic antigen (CEA) in colorectal cancer patients--with particular emphasis on the correlation between immunoreactive CEA levels in tissue, feces and blood.

Immunoreactive carcinoembryonic antigen (IR-CEA) levels in colorectal cancer and mucosal tissues, feces and blood were measured in 14 colorectal cancer patients to study the correlation. IR-CEA levels in colorectal cancer tissues were about 30 times higher than those in colonic mucosal tissues. The correlation coefficient between IR-CEA levels in the tumor tissue and serum was 0.654 (p less than 0.02). We assumed that the total tumor IR-CEA levels were the product of the tumor IR-CEA level, by the estimated tumor weight. The correlation coefficient between the serum IR-CEA level and total tumor IR-CEA level was 0.750 (p less than 0.001). When the patients were divided into two groups with more and less a total tumor IR-CEA level of 65,000 ng, respectively, the statistical difference in serum IR-CEA levels was p less than 0.001. The differences in fecal IR-CEA levels between these two groups, however, are statistically insignificant (p less than 0.3). We assumed that there was a positive correlation between the IR-CEA levels in blood and tumor from the consideration that circulating IR-CEA originates from the metabolic imbalance of its production in colorectal cancer tissues over its degradation in the liver. Moreover, it is essential to consider that the fecal IR-CEA levels may be influenced by the following three factors: the intraluminal direct release of CEA from tumor, no degradation process of CEA in the gut lumen, and the intraluminal transport rate of colonic contents.