Organ Specificity and Tumor Promotion

Abstract

The modification of experimental carcinogenesis by agents that are not carcinogenic alone has been studied for over 40 years. Much attention has centered on compounds termed tumor promoters. Tumor promoters cause or allow the expression of the latent tumor phenotype induced in some cells by limited doses of carcinogens. Both chemical and physical stimuli can act as tumor promoters. Interest in tumor promotion is appropriate since this phase of carcinogenesis accounts for most of the latent period. For many years research in tumor promotion was confined to studies in mouse skin and limited to the use of impure reagents such as croton oil. During the last decade, broad interest in this aspect of carcinogenesis has developed largely due to the discovery of specific agents that act as tumor promoters and to the development of experimental models other than mouse skin in which promotionlike events contribute to tumor formation. Perhaps of equal importance, epidemiological studies in human cancer have suggested that a promotion phase is important in lung cancer, colon cancer, and cancer in hormonall-egulated target tissues.