Carcinogen
Carcinogen, any chemical, biological, or physical agent that can potentially be a cause of cancer. The term is most commonly applied to chemicals introduced into the environment by human activity. Researchers label a substance a carcinogen if it causes a statistically significant increase in some form of neoplasm, or anomalous cell growth, when applied to a population of previously unexposed organisms. The modes of cancer initiation are still little understood, however, and efforts to establish the carcinogenic hazards of substances have aroused great controversy. The question of the usefulness of laboratory tests on animals in assessing human risks is particularly complex. The more recent development of short-term tests using cell cultures of microorganisms, however, is considered a major advance in carcinogen research. Substances indicted as carcinogenic over the past few decades include the pesticides DDT, Kepone, and EDB; the synthetic hormone DES; the artificial sweetener cyclamat