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Toxicological Sciences 55, 3-16 (2000)
Copyright © 2000 by the Society of Toxicology

Forum

Reevaluation of the Cancer Potency Factor of Toxaphene: Recommendations from a Peer Review Panel

Jay I. Goodman*,1, David J. Brusick{dagger}, William M. Busey{ddagger}, Samuel M. Cohen§, James C. Lamb,2 and Thomas B. Starr||

* Department of Pharmacology and Toxicology, Michigan State University, E. Lansing, Michigan; {dagger} Covance Laboratories, Inc., Vienna, Virginia; {ddagger} Experimental Pathology Laboratories, Inc., Herndon, Virginia; § Department of Pathology and Microbiology, University of Nebraska, Omaha, Nebraska; Jellinek, Schwartz, & Connolly, Inc., Arlington, Virginia; and || Environ, Raleigh, North Carolina

ABSTRACT

This reevaluation of the current U.S. EPA cancer potency factor for toxaphene is based upon a review of toxaphene carcinogenesis bioassays in mice conducted by Litton Bionetics (unpublished report, 1978) and the National Cancer Institute (NCI) (Technical Report Series No. 37, conducted by Gulf South Research Institute, 1979). The mechanistic data available for toxaphene, including consideration of the potential of the compound to induce genotoxicity, was examined with an emphasis on whether this information supports a change in the cancer potency factor. If a quantitative dose-response assessment for toxaphene is to be performed, the data from both the NCI and Litton cancer bioassays should be used. Additionally, liver tumor results from female mice, rather than male mice, should be used for estimating potential human cancer risk because the background rate of liver tumors in females is lower and less variable than that exhibited by males. An ED10 was estimated as the point of departure. The mechanistic data were not sufficient to fully support a margin of exposure approach. Therefore, we believe that applying a linear extrapolation from the ED10 to the origin is an appropriate means to estimate risk at low doses. This is a highly conservative approach and, when it is applied, we conclude that the current EPA cancer potency factor should be reduced from 1.1 (mg/kg/day)–1 to 0.1 (mg/kg/day)–1.

Key Words: toxaphene; cancer potency factor; margin of exposure; pathology working group (PWG).


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