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Carcinogen risk assessment in the U.S. Environmental Protection Agency.

This is a narrative account of the origins and development of carcinogen risk assessment in the U.S. EPA, which pioneered the field. It began in an era of high hopes that the regulation of carcinogens in the environment would make a major reduction in the heavy public health burden of cancer. The immediate cause for the development of carcinogen risk assessment was the need to respond to heavy criticism that the EPA was not using science in an unbiased way to defend its regulation of important pesticides as carcinogens. The formulation of the initial assessment guidelines is described as well as the rationale behind the assessment procedures that were developed by the EPA's Carcinogen Assessment Group. The issue of whether the original hopes of reducing cancer has been realized is discussed. Recent developments in molecular carcinogenesis point to the possibility of a revised view of the role of environmental carcinogens at low levels of exposure from that of causing cancer de novo to an acceleration of the development of cancer that results from heritable genetic defects. It is suggested that advances in carcinogen risk assessment will mainly depend on a better understanding of the causes and mechanisms of cancer in humans at the molecular level.