Cocarcinogens and Tumor Promoters and Their Environmental Importance

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Abstract
In recent years a great deal of effort has been spent on uncovering new carcinogens and studying the mode of action of well-known carcinogens such as nitroso compounds, aromatic hydrocarbons and aromatic amines and their occurrence in air, water, foods and other environmental sources. It has been known for about thirty years that some materials, while non-carcinogenic, can enhance greatly the potency of low-levels of known environmental carcinogens. The first such material to be discovered was the tumor promotor, croton oil, derived from the seeds of a tropical plant, Croton tiglium L, indigenous to India and Sri Lanka. Researchers interested in chemical carcinogenesis have examined its unusual behavior for many years. The active principles of croton oil, the phorbol esters, were finally isolated and chemically characterized. Recently these phorbol esters have become widely available. Consequently, their effects have been examined in a wide range of biochemical and biological studies. The phorbol esters are not environmental factors in cancer causation since they occur in a toxic plant which is not used as a source of animal or human food. Other known tumor promoters are much less active, e.g., anthralin (1,8-dihydroxy-9-anthrone) and phenol. Thus, the phorbol esters, although valuable tools in studies on chemical carcinogenesis, are less relevant to environmental health and disease than another group of compounds known as cocarcinogens. Many cocarcinogens are ubiquitous environmental agents and only recently have these compounds been given more attention. It is expected that as more of these agents become known as environmental agents, new advances in cancer prevention will be made.