Carcinogenesis: Mechanisms and Models

Abstract The three main classes of agents causing cancers are chemicals, radiation, and viruses. Development of cancer is a multistep process; the steps are initiation, promotion, and progression. The International Agency for Research on Cancer has classified carcinogens into five groups: Group 1 (known carcinogen), Group 2A (probable carcinogen), Group 2B (possible carcinogen), Group 3 (not classifiable as a carcinogen), and Group 4 (not carcinogenic). Tests most frequently used to determine the carcinogenic activity of a compound include long-term bioassays and short-term assays. Building of databases of known/suspected carcinogenic compounds has helped in the development of computer programs that can predict the carcinogenic potential of new compounds using quantitative structure-activity relationships. These programs provide additional tools when there is ambiguous data or insufficient data to infer safety.