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James Huff,¹ Michael F. Jacobson,² and Devra Lee Davis³

¹National Institute of Environmental Health Sciences, National Institutes of Health, Department of Health and Human Services, Research Triangle Park, North Carolina, USA; ²Center for Science in the Public Interest, Washington, DC, USA; ³Center for Environmental Oncology, University of Pittsburgh Cancer Institute, Department of Epidemiology, Graduate School of Public Health, Pittsburgh, Pennsylvania, USA

Abstract
Background: Chemical carcinogenesis bioassays in animals have long been recognized and accepted as valid predictors of potential cancer hazards to humans. Most rodent bioassays begin several weeks after birth and expose animals to chemicals or other substances, including workplace and environmental pollutants, for 2 years. New findings indicate the need to extend the timing and duration of exposures used in the rodent bioassay.

Objectives: In this Commentary, we propose that the sensitivity of chemical carcinogenesis bioassays would be enhanced by exposing rodents beginning in utero and continuing for 30 months (130 weeks) or until their natural deaths at up to about 3 years.

Discussion: Studies of three chemicals of different structures and uses—aspartame, cadmium, and toluene—suggest that exposing experimental animals in utero and continuing exposure for 30 months or until their natural deaths increase the sensitivity of bioassays, avoid false-negative results, and strengthen the value and validity of results for regulatory agencies.

Conclusions: Government agencies, drug companies, and the chemical industry should conduct and compare the results of 2-year bioassays of known carcinogens or chemicals for which there is equivocal evidence of carcinogenicity with longer-term studies, with and without in utero exposure. If studies longer than 2 years and/or with in utero exposure are found to better identify potential human carcinogens, then regulatory agencies should promptly revise their testing guidelines, which were established in the 1960s and early 1970s. Changing the timing and dosing of the animal bioassay would enhance protection of workers and consumers who are exposed to potentially dangerous workplace or home contaminants, pollutants, drugs, food additives, and other chemicals throughout their lives.

Key words: animal cancer tests, aspartame, bioassay designs, bisphenol A, cadmium, carcinogenicity, chemical carcinogens, genistein, toluene, toxicology. Environ Health Perspect 116:1439–1442 (2008) .  doi:10.1289/ehp.10716 available via http://dx.doi.org/ [Online 30 June 2008]

Address correspondence to M.F. Jacobson, Center for Science in the Public Interest, 1875 Connecticut Ave., Suite 300, Washington, DC 20009 USA. Telephone: (202) 777-8328. Fax: (202) 265-4954. E-mail: mjacobson@cspinet.org

M.F.J. is employed by an advocacy organization that supports stronger testing protocols for chemicals in food. The other authors declare they have no competing financial interests.

Received 28 July 2007 ; accepted 30 June 2008.