Any substance that causes the development of cancerous growths in living tissue. Such substances are usually grouped in two classifications: (1) those that are known to induce cancer in humans or animals, either by operational exposure in industry or by ingestion in feedstuffs, e.g., asbestos particulates, nickel carbonyl, trichloroethylene, benzidine and compounds, vinyl monomer, benzopyrene, aflatoxin, chloromethyl ether, β-naphthylamine, as well as anthracene, phenanthrene, chrysene, and other polynuclear hydrocarbons of coal tar origin; (2) experimental carcinogens that have been found to cause cancer in animals under experimental conditions, namely, by external applications, feeding, or injection of the substance. Among these are dimethyl sulfate, cyclamate compounds, ethyleneimine, and 4-dimethylaminoazobenzene. The Delany amendment to the Food, Drug, and Cosmetic Act forbids the use in human foods of any substance falling in this group. The substances mentioned above by no means comprise a complete list of carcinogens. There are approximately 3500 known and suspected carcinogenic compounds, and new ones are constantly being discovered.
