Viroimmunoassay utilizing a synthetic peptide: a test equivalent to the carcinoembryonic antigen radioimmunoassay

A recently developed immunoassay which utilizes the synthetic fragment CEA(1-11), corresponding to the N-terminal segment of carcinoembryonic antigen (CEA), was used for the evaluation of human sera. The various sera were tested for their capacity to inhibit the inactivation of the modified bacteriophage preparation CEA(1-11)-T4 by antiserum prepared against the bovine serum albumin (BSA) conjugate CEA(1-11)-BSA. In this immunological system both the free synthetic peptide and a semipurified preparation of intact CEA serve as inhibitors. Sera from a large proportion (85%) of patients with adenocarcinomas of the digestive tract, including the pancrease, gave 50 to 88% inhibition. Sera from patients with other cancers, particularly of breast and ovary, also caused inhibition, although it was less marked in both incidence and level. Most normal sera gave less than 40% inhibition, which was considered as the cutoff point. This assay, like the CEA radioimmunoassay, is not suitable for mass screening nor can it be the primary criterion for diagnosis of cancer, but it might be of value as a follow-up procedure for postoperative diagnosis and prognosis.