Radioimmunoassay of carcinoembryonic antigen in serum of normal subjects and patients with colonic carcinoma.

Sera from 14 normal subjects and 43 patients with colonic carcinoma were evaluated for the presence of carcinoembryonic antigen (CEA). Inhibiting material which behaved in the assay in a similar manner to CEA was found in normal serum at concentrations below 2.8 ng/ml. Its nature has not so far been established. Thirty-eight of the 43 patients with colonic carcinoma showed levels of serum CEA in excess of 2.8 ng/ml. The concentration of CEA in serum was correlated with the extent of the disease as classified by a staging procedure similar to that of Dukes (1932). Examination of a small number of specimens of colonic carcinoma and normal colonic mucosa suggested that the concentration of CEA in different adenocarcinomata may vary, and that traces of cross-reacting material may be found in some normal mucosae.