Carcinogen

A carcinogen is an agent, mixture, or exposure that increases the occurrence of cancer. Carcinogen identificationisanactivitybasedontheevaluationofthe results of scientific research. Pertinent data for carcinogen identification include human epidemiologic studies, long-term bioassays in experimental animals, and other relevant data on toxicokinetics and cancer mechanisms. Several classification systems exist to identify the degree of carcinogenicity of agents. The most widely used system is developed by the International Agency for Research on Cancer (IARC), which is part of the World Health Organization.

Most of the existing data about whether an agent might cause cancer originate from laboratory (cell culture and animal) studies. Although it is not possible to predict with certainty which substances will cause cancer in humans based on animal studies alone, virtually all known human carcinogens that have been adequately tested have been found to produce cancer in lab animals. In many cases, carcinogens are first found to cause cancer in lab animals and are later found to cause cancer in humans. For most carcinogens, it is assumed that those that cause cancer at larger doses in animals will also cause cancer in humans.

Another source of data about carcinogens comes from epidemiologic studies, which provide evidence of a carcinogenic hazard but often are not sufficiently sensitive to identify a carcinogenic hazard except when the risk is high or when it involves an unusual form of cancer. In addition, it is difficult to single out any particular exposure as having a definite link to cancer. For these reasons, laboratory studies generally provide the best means of assessing potential risks to humans.