Tumor Markers and Their Relevance in the Design of Radioimmunoimaging Experiments

Abstract

The dream of an immuno-oncologist is to define precise epitopes of tumor-specific markers. That of a nuclear medicine physician is to identify a reliable, reproducible, system not only for the imaging of tumors but also to prognosticate on the course of disease in the patient and between these two expectations is the realm of immunoscintigraphy. Histopathologic and serologic identification of neoplasia as well as the monitoring of their treatment can be effected through their tumor-associated markers. The latter have been classified as oncofetal protein antigens, enzymes, hormones, polyamines, or unusual or unexpected carbohydrate antigens. The production of the markers varies during the natural progression of malignancy and may correlate with its aggressiveness. Despite the complexities related to the conditions of appearance and disappearance of such markers in patient sera, certain tumor markers may be more constant in their behavior. An excellent summation of the status of such markers in clinical practice has been presented by Colnaghi et al. (1). Our group has been interested in carbohydrate expression on cancer cells which display dramatic changes in the composition and architecture of cell surface glycoproteins and glycolipids and which are recognized by the immune system. These cell surface carbohydrate antigens are known to participate in important cell-cell interactions and the regulation of cell growth and differentiation (2,3). Aberrant expression of carbohydrate antigens on malignant cells is well documented and may play an important role in maintaining the malignant phenotype (4). Moreover, the expression of new carbohydrate determinants on malignant cells, found only in very low concentrations on some normal cells, may represent important markers 1) to study their role in malignancy, 2) for early detection of cancer, 3) for the management of cancer patients, 4) for prognosis and 5) for cancer immunotherapy. Table 1 summarizes some of the important carbohydrate antigens which have been associated with a number of human cancers.