[A radioimmunometric assay for circulating tumor-associated glycoprotein (TAG-72) using the antigen determinant CA 72-4].

Tumor-associated glycoprotein (TAG-72) is an antigen recognized by monoclonal antibody (MAb) B 72.3 which was generated against a membrane enriched fraction of human mammary carcinoma cells. CA 72-4 is a novel antigen determinant on TAG-72 and is a quantitative radioimmunometric assay system utilizing two MAbs (CC-49, B 72.3) which react with circulating TAG-72 expressed by human carcinomas. We have employed the CA 72-4 RIA system to measure the antigen in sera. The optimum condition for this assay was found to be a 4 hour incubation at 37 degrees C for the first reaction and a 20 hour incubation at 4 degrees C for the second reaction. Under these conditions, intra-assay variation of the control sera was C.V. 3.0-5.2% and inter-assay variation was 5.6-8.3%. The mean +2 SD of CA 72-4 concentration in 468 healthy persons was 3.9 U/ml. Therefore, less than 4.0 U/ml was taken as the cut off level for the CA 72-4 serum assay. The largest population in healthy persons was at the range of 1.5-2.0 U/ml. Only 15 of 468 persons (3.2%) demonstrated serum CA 72-4 levels more than 4.0 U/ml. These data thus indicate the efficacy of CA 72-4 RIA system for the serum assay as a novel tumor marker. The clinical evaluation of CA 72-4 in patients with epithelial malignancies is now underway.