SUMMARY Carcinoembryonic antigen (CEA) levels have been measured in the serum of 490 patients and 93 normal controls using the double antibody radioimmunoassay technique. Levels were elevated in 71 of patients with carcinomata of the gastrointestinal tract and in 42% with other types of malignancy. In patients with non-neoplastic disease of the gastrointestinal tract and liver, elevated levels were found in 14 and 66 % respectively. In general the CEA level tends to be higher in cancer patients with haematogenous dissemination. Following complete surgical removal of a tumour, levels fall to normal within 14 days in the majority of patients. Of 33 patients studied during follow up, elevated levels were found in 12, 10 of whom had evidence of recurrence.The significance of these findings and the possible application of CEA assay in clinical practice are discussed.In recent years many attempts have been made to detect macro-molecular substances specific for human tumours, which if liberated into the body fluids could form the basis of an assay useful in the early diagnosis and management of malignant disease. One of the best such examples is the assay of chorionic gonadotrophin in patients with choriocarcinomata (Bagshawe, 1969).Well documented evidence has existed for some time of specific antigens in experimentally induced tumours of animals (Old, Boyse, Clarke, and Carswell, 1962 (Gold and Freedman, 1965a). They later detected the same antigen in extracts of other gastrointestinal carcinomata together with extracts of foetal intestine, liver, and pancreas during the first two trimesters of pregnancy (Gold and Freedman, 1965b colon (Martin and Martin, 1970) and pooled normal serum (Chu, Reynoso, and Hansen, 1972). This change in view of the specificity of CEA is reflected in the reports of radioimmunoassay results in a wide range of clinical groups. An initial claim of 97% positivity in patients with carcinoma of the colon
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