A collaborative study of a test for carcinoembryonic antigen (CEA) in the sera of patients with carcinoma of the colon and rectum. A joint National Cancer Institute of Canada-American Cancer Society investigation.

Five university centres in Canada and the United States have collaborated in a study of a test for carcinoembryonic antigen, with the Montreal General Hospital laboratory acting as the reference laboratory, examining duplicate halves of specimens from patients examined in local laboratories.Between June 1971 and April 1972, 503 patients were admitted to the study, 146 with cancer of the colon or rectum. Discrimination between colo-rectal cancer and "other" diagnoses was good at 2.5 ng./ml. or more, such a result being obtained in 66% of the patients with colo-rectal cancer in the local laboratories and 62% in the reference laboratory compared with 39% and 33% respectively of patients with "other" diagnoses. Patients with Duke's C lesions of the colon or rectum were more likely to have raised CEA levels than patients with more localized lesions. CEA was also more commonly found in patients with other cancers and in patients with liver disease than in patients with other (benign) diagnoses.It is concluded that the test can be reproduced in other laboratories and that it or another simplified technique could become an important diagnostic aid for colo-rectal cancer.