Comparative studies on the radioimmunological determination of carcinoembryonic antigen in tumour tissue

Human carcinoembryonic antigen (CEA) was measured in perchloric acid extracts from 9 malignant gastrointestinal tumours, using two different radioimmunological methods (Hoffmann-La Roche and CEA-IRE-SORIN). When standard curves were set up, quantitative differences in the degree of inhibition were found between the standards from the two manufacturers. In the Hoffmann-La Roche assay the CEA binding curves of all tumour extracts ran parallel with the standard. However, when the CEA-IRE-SORIN assay was applied two of the nine tumours exhibited different slopes. In one case, using the CEA-IRE-SORIN method, various parts of the tumour exhibited binding curves with non-parallel slopes. The present results suggest that radioimmunologically heterogeneous CEA occurs in different gastrointestinal tumours as well as in various parts of the same tumour.