CA 72-4 radioimmunoassay for the detection of the TAG-72 carcinoma-associated antigen in serum of patients

Monoclonal antibody (MAb)B72.3 has been used to detect the presence of TAG-72 in the serum of carcinoma patients. We have developed new anti-TAG-72 MAbs and have selected one of these, CC49, as the 'catcher' MAb with ¹²⁵I-B72.3 as the detecting antibody in a double-determinant immunoradiometric assay. This combination enabled the development of a sequential assay (designated CA 72-4) that showed optimal quantitative properties as demonstrated by such parameters as linear dose-response, high reproducibility, and lack of serum-matrix and 'hook-back' effects. Only 3.5% of 744 normal sera and 6.7% of 134 sera from patients with benign gastrointestinal diseases had TAG-72 levels greater than 6 U/ml. Approximately 40% of 303 patients with gastrointestinal malignancies had serum TAG-72 levels of greater than 6 U/ml (55% of the patients with advanced disease). Thirty-six percent of patients with adenocarcinomas of the lung and 24% of patients with ovarian cancer (53% stage IV patients) also had elevated serum TAG-72 levels. A poor correlation was found between the carcinoembryonic antigen (CEA) and TAG-72 values of sera obtained from gastric cancer patients. Thirty-four percent of CEA negative cases were scored positive in the CA 72-4 assay, suggesting the complementarity of the CA 72-4 assay to CEA assays in the analysis of sera from patients with certain malignancies.