Comparison of serum assays for TAG-72, CA19-9 and CEA in gastrointestinal carcinoma patients

Tumor-associated glycoprotein (TAG-72) has been shown to be expressed in a wide variety of epithelial malignant tissues. We have investigated serum levels of TAG-72 antigen in patients with gastrointestinal cancer with a solid phase radioimmunometric assay (RIA), CA72-4, utilizing murine monoclonal antibodies CC49 and B72.3 which recognize the TAG-72 antigen. Elevated levels of serum TAG-72 antigen were found in 48% of 56 gastric carcinoma patients and 67% of 45 colorectal carcinoma patients. The serum concentrations of TAG-72 were compared to those of CA19-9 and CEA. The positive rates of CA19-9 in gastric carcinoma and colorectal carcinoma patients were 29% and 54%, and those of CEA were 52% and 60%, respectively. Elevated serum levels of TAG-72, CA19-9 and CEA were observed in 7%, 14% and 24%, respectively, of patients with benign disease, thus indicating a preferential expression of TAG-72, compared to CA19-9 and CEA, in gastrointestinal carcinoma patients versus in patients with benign disorder. A cocktail of CA72-4, CA19-9 and CEA RIAs increased positive rates to 68% in sera of gastric cancer patients and 84% in sera of colorectal cancer patients. Combination assays using CA72-4, CEA and CA19-9 RIAs for patients with benign gastrointestinal disorder, however, also increased the positive rate to 31%. These results indicate that CA72-4, CA19-9 and CEA RIAs may be complementary in detecting circulating tumor-associated antigens. It must be emphasized, however, that interpretation of the data provided by the combination serum assays requires careful consideration.