Reviews/Übersichten

Abstract

Qualitative differences between normal cells and tumour cells have been demonstrated in animal models using immunological methods. So far, no soluble tumour-specific antigens have been found in man. Only quantitative differences between normal and malignant cells were detected for the following soluble antigens: foetal antigens, tumour-associated hormones and tumour-associated enzymes. Of these, carcinoembryonic antigen (CEA), a-fetoprotein (AFP) and human chorionic gonadotropin (HCG) are of limited diagnostic significance.CEA occurs in numerous normal and inflamed tissues, in benign and malignant tumours, and in various body fluids; this indicates that CEA lacks tumour specificity. The biochemical heterogeneity of CEA is primarily due to its carbohydrate moiety, whereas the antigenic determinants are probably localised on the protein moiety of the molecule. Therefore, attempts to utilise biochemical heterogeneity for the isolation of CEA fractions possessing higher specificity in radioimmunoassay have been unsuccessful. Due to the low affinity to the antibodies, antigens like normal crossreacting antigen (NCA) which show cross reaction with CEA in immunodiffusion do not affect the radioimmunological determination of CEA. Contradictory results have been reported for the correlation between the differentiation of a tumour and its CEA concentration. On the other hand, high concentrations of CEA in serum could be correlated with poorly differentiated and infiltrative tumours. From the results, so far reported in the literature, it is clear that the determination of CEA in serum is not suitable for the primary diagnosis of a cancer; however, CEA has been successfully used in follow-up studies as an indicator of metastases or the recurrence of a tumour.