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Issues in Risk Assessment (1993)

Chapter: BACKGROUND

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Suggested Citation:"BACKGROUND." National Research Council. 1993. Issues in Risk Assessment. Washington, DC: The National Academies Press. doi: 10.17226/2078.
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Appendixes

Appendix A
Workshop Summary Maximum Tolerated Dose: Implications For Risk Assessment

INTRODUTION

This report summarizes the discussions at a workshop held by the Committee on Risk Assessment Methodology on September 6, 1990, in Washington, DC. An agenda and a list of presenters, discussants, and other participants are appear in Appendixes D and E.

BACKGROUND

Current testing for carcinogenicity in laboratory animals involves testing both sexes of rats and mice for 2 years (nearly a lifetime) at an estimate of the maximum tolerated dose (MTD) and usually at one or more lower doses. The MTD is defined generally as the highest dose of the test agent that is predicted not to alter the animals' longevity or growth because of noncancer effects. The MTD thus varies inversely with the toxicity of a chemical.

A number of researchers have investigated correlations between the MTD and various measures of carcinogenic potency. Some have concluded that the correlations have a biologic basis and might be indicating something general about mechanisms of carcinogenesis. Others have

Suggested Citation:"BACKGROUND." National Research Council. 1993. Issues in Risk Assessment. Washington, DC: The National Academies Press. doi: 10.17226/2078.
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The scientific basis, inference assumptions, regulatory uses, and research needs in risk assessment are considered in this two-part volume.

The first part, Use of Maximum Tolerated Dose in Animal Bioassays for Carcinogenicity, focuses on whether the maximum tolerated dose should continue to be used in carcinogenesis bioassays. The committee considers several options for modifying current bioassay procedures.

The second part, Two-Stage Models of Carcinogenesis, stems from efforts to identify improved means of cancer risk assessment that have resulted in the development of a mathematical dose-response model based on a paradigm for the biologic phenomena thought to be associated with carcinogenesis.

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