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Toxicological Sciences 58, 416 (2000)
Copyright © 2000 by the Society of Toxicology

Letters to the Editor

Letter

Lubow Jowa and John Faust

California Environmental Protection Agency, Office of Environmental Health Hazard Assessment, 301Capitol Mall, Rm. 205 Sacramento, CA 95814-4308

To the Editor:

We wish to comment on "Reevaluation of the Cancer Potency Factor of Toxaphene: Recommendation from a Peer Review" by Goodman et al. (Toxicological Sciences 55, 3–16).

The cancer potency derived by Goodman et al. is approximately 10-fold lower than values previously derived by the U.S. Environmental Protection Agency and California. In spite of using a different extrapolation model and reevaluated data, much of the difference between the potencies results from the selection of the female mouse liver tumor data over that from males, because "the background rate of liver tumors in females is lower and less variable than that exhibited by males." The variability in male control data is low, with incidences of 19, 20, and 15% in the Litton, National Cancer Institute (NCI) (matched), and NCI (pooled) groups, respectively. We agree that the background liver tumor incidence is higher in control males than in females; however, this does not introduce "considerable uncertainty." Curve fitting readily accommodates the higher background rate. Given the substantially greater sensitivity of the male mouse compared to the female mouse, this level of "uncertainty" should not rule out the use of the male data as the basis for the risk assessment.

The authors also suggest that the Litton tumor data evaluation would not hold up under current diagnostic criteria, yet later, in noting that the pattern of reassessed NCI tumor types is "in line" with the Litton data, they justify combining the data sets. We believe it is contradictory to question the qualitative aspects of the Litton tumor evaluation and then to accept the data as suitable for a combined quantitative risk assessment.


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This Article
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