SURVEILLANCE MECHANISMS AND MALIGNANCY

Abstract

This chapter describes surveillance mechanisms for malignancy. Chemical and physical agents with oncogenic properties are widespread in the environment. Oncogenic viruses are often transmitted vertically in embryogenesis or soon after gestation in mother's milk. The natural development of cancer in humans and experimental animals is surprisingly infrequent in the face of such intensive and frequent exposure to oncogenic agents. Control mechanisms in single cells may provide a form of surveillance against malignant transformation. These mechanisms appear to be largely under genetic control, as demonstrated in inbreeding and somatic cell hybridization studies. Of probable importance are enzymes responsible for inactivation of chemical carcinogens, enzymes responsible for DNA repair, and regulatory genes and repressor proteins. These intracellular surveillance mechanisms have the capacity to prevent or reverse malignant transformation by oncogenic agents. Viral transformation assays in vitro have been useful in the study of host defense mechanisms, especially as an aid in the disection of these mechanisms into intracellular and intercellular components. The assays allow direct inoculation of viruses and chemicals into cultured cells. Transformation susceptibility can be frequently quantitated and, in certain instances, correlated with the individual's risk of malignancy.