Bioassay protocols for identifying chemical carcinogens have recommended extending the duration of rodent studies to ≥ 30 months (Davis 2007; Haseman et al. 2001; Huff 2002; Huff et al. 2007; Maltoni 1995; Soffritti et al. 2002). In some cases, as the Ramazzini Foundation some- times does, exposure to industrial chemicals is stopped after 2 years (“retirement age”), and the animals are then observed until ≥ 30 months of age to determine delayed or persistent carcino- genic activity (Maltoni 1995; Soffritti et al. 2002). Ceasing exposure at 2 years without monitoring tumor development for additional time cannot estimate the impact of food addi- tives, drugs, and other chemicals on humans who die in their 70s or later. Advantages of 2-year studies over studies with longer observation periods. Two-year studies do have certain advantages over longer studies. First, because these studies are stan- dard protocols and designs, a great deal of experience has been gained from them, including information on tumor formation in historical controls. Second, these briefer studies yield some- what quicker results, which is useful for pro- tecting public health. Third, shorter tests are somewhat, but not proportionately, cheaper to conduct. However, because of the numerous ﬁxed costs of animal studies (animals, postmortem pathology, etc.), longer studies are not commensurately margin- ally costlier. In any case, economy should not trump sensitivity and the reliability of results. Ancillary costs of longer studies include educating researchers on how to conduct them and carrying out more frequent inspections at the later stages for moribund or sickly animals to minimize autolysis in animals that die natu- rally at night and may not be discovered immediately. However, certain tissues are affected more than others, and tumors would remain relatively inviolate; moreover, even in 2-year studies, only 60–70% of animals remain alive at the end. Fourth, some tumor rates increase, and old-age lesions may complicate discerning nonneoplastic effects. Finally, whereas tumor incidences in vari- ous strains of control animals are known on the basis of numerous studies, it would take time to develop a body of data on tumor inci- dence and other abnormalities for these longer time periods. Some researchers have argued that higher rates of spontaneous tumors and other factors would undermine the value of longer-term studies (Solleveld and McConnell 1985), but those assertions are not based on actual bio- assays—comparing, for instance, the relative abilities of 24-month, 30-month, and life- time bioassays to detect the effects of known carcinogens. Most important, any “savings” accruing from current testing protocols are only illusory if false-negative results lead to the exposure of millions of people to sub- stances that caused cancer or other maladies. To maximize the knowledge gained from costly full-lifetime studies, protocols should be expanded to provide for periodic sacriﬁcing to determine time-to-tumor and biological sam- pling to determine internal doses, metabolite levels, genetic alterations, and other data rele- vant to characterizing the pharmacokinetic and pharmacodynamic activity of toxicity and noncancer disease. Conclusion The evidence presented here indicates that extending animal bioassays beyond 2 years and beginning exposure in utero, especially for endocrine-disrupting chemicals that “act” preferentially in early life (Huff 1996, 2001; Huff et al. 1996; Newbold et al. 2001; Newbold and McLachlan 1982; Thayer and Foster 2007; Tomatis et al. 1992; Yamasaki et al. 1992), would provide more reliable and appropriate indicators of human risk. The FDA, U.S. Environmental Protection Agency, Occupational Safety and Health Administration, Consumer Product Safety Commission, NTP, and others should recon- sider their designs of “best practices” regarding long-term studies of chemicals for detection of carcinogenic risks to humans. We urge those governmental agencies, perhaps in conjunction with such other agencies as the World Health Organization’s International Agency for Research on Cancer, to conduct and compare the results of 2-year and longer-term feeding studies, with and without in utero exposure, of known or equivocal-evidence carcinogens. It is noteworthy that the FDA already “recommends that in utero exposure be included in carcinogenicity studies due to the fact that exposure to food ingredients occurs during all stages of life” (FDA 2006). If bio- assays demonstrate that studies longer than 2 years and/or with in utero exposure are better able to identify carcinogens, regulatory agen- cies should revise their testing guidelines, most of which were established > 40 years ago (Bucher 2002; Huff and Moore 1984; Weisburger 1983). Another gap in regulatory protocols involves male-mediated teratogenesis—the study of compounds’ capacity to impede repro- ductive health of offspring through paternal genomic and other male-mediated routes (Davis et al. 1992). Regarding endocrine disruptors and other chemicals that cross the placenta and affect critical windows of develop- ment, one need not wait for comparison bio- assays before routinely conducting in utero and longer-term bioassays. Beneﬁts to public health from conducting more sensitive bioassays that reﬂect early life exposures and continue throughout a natural lifetime of observation could be considerable. Environmental Health Perspectives • VOLUME 116 | NUMBER 11 | November 2008 REFERENCES Abdo KM, Camargo CA Jr, Davis D, Egilman D, Epstein SS, Froines J, et al. 2007. Letter to U.S. FDA commissioner. Questions about the safety of the artificial sweetener aspartame [Letter]. Int J Occup Environ Health 13:449–450. Abdo KM, Kari FW. 1996. The sensitivity of the NTP bioassay for carcinogen hazard evaluation can be modulated by dietary restriction. Exp Toxicol Pathol 48(2–3):129–137. Belpoggi F, Soffritti M, Padovani M, Degli Esposti D, Lauriola M, Minardi F. 2006. Results of long-term carcinogenicity bio- assay on Sprague-Dawley rats exposed to aspartame administered in feed. Ann NY Acad Sci 1076:559–577. Bucher JR. 2002. The National Toxicology Program rodent bioassay: designs, interpretations, and scientiﬁc contribu- tions. Ann NY Acad Sci 982:198–207. Committee on Toxicity Testing and Assessment of Environmental Agents, Board on Environmental Studies and Toxicology, National Research Council. 2007. Toxicity Testing in the Twenty-First Century: A Vision and a Strategy. Washington, DC:National Academies Press. Dairkee SH, Seok J, Champion S, Sayeed A, Mindrinos M, Xiao W, et al. 2008. Bisphenol A induces a proﬁle of tumor aggressiveness in high-risk cells from breast cancer patients. Cancer Res 68:2076–2080. Davies TS, Lynch BS, Monro AM, Munro IC, Nestmann ER. 2000. Rodent carcinogenicity tests need be no longer than 18 months: an analysis based on 210 chemicals in the IARC Monographs. Food Chem Toxicol 38:219–235. Davis DL. 2007. The Secret History of the War on Cancer. New York:Basic Books. Davis DL, Friedler G, Mattison D, Morris R. 1992. Male-mediated teratogenesis and other reproductive effects: biologic and epidemiologic findings and a plea for clinical research. Reprod Toxicol 6:289–292. Dolinoy DC, Huang D, Jirtle RL. 2007. Maternal nutrient supple- mentation counteracts bisphenol A-induced DNA hypomethylation in early development. Proc Natl Acad Sci USA 104:13056–13061. FDA (Food and Drug Administration). 2006. Toxicological Principles for the Safety Assessment of Food Ingredients. Available: http://www.cfsan.fda.gov/~redbook/red-ivc6.html [accessed 24 January 2008]. Haseman J, Melnick R, Tomatis L, Huff J. 2001. Carcinogenesis bioassays: study duration and biological relevance. Food Chem Toxicol 39:739–744. Herbst AL, Ulfelder H, Poskanzer DC. 1971. Adenocarcinoma of the vagina. Association of maternal stilbestrol therapy with tumor appearance in young women. N Engl J Med 284:878–881. Huff J. 1996. Chemically induced cancers in hormonal organs of laboratory animals and of humans. Prog Clin Biol Res 394:77–102. Huff J. 1999. Value, validity, and historical development of car- cinogenesis studies for predicting and conﬁrming carcino- genic risks to humans. In: Carcinogenicity Testing, Predicting, and Interpreting Chemical Effects (Kitchin KT, ed). New York:Marcel Dekker, 21–123. Huff J. 2001. Carcinogenicity of bisphenol-A in Fischer rats and B6C3F1 mice. Odontology 89:12–20. Huff J. 2002. Chemicals studied and evaluated in long-term car- cinogenesis bioassays by both the Ramazzini Foundation and the National Toxicology Program: in tribute to Cesare Maltoni and David Rall. Ann NY Acad Sci 982:208–230. Huff J. 2003. Absence of carcinogenic activity in Fischer rats and B6C3F1 mice following 103-week inhalation exposures to toluene. Int J Occup Environ Health 9:138–146. Huff J, Boyd J, Barrett JC. 1996. Hormonal carcinogenesis and environmental inﬂuences: background and overview. Prog Clin Biol Res 394:3–23. Huff J, LaDou J. 2007. Aspartame bioassay findings portend human cancer hazards. Int J Occup Environ Health 13:446–448. Huff J, Lunn RM, Waalkes MP, Tomatis L, Infante PF. 2007. Cadmium-induced cancers in animals and in humans. Int J Occup Environ Health 13:202–212. Huff J, Moore JA. 1984. Carcinogenesis studies design and experimental data interpretation/evaluation at the National Toxicology Program. Prog Clin Biol Res 141:43–64. Ishii H, Koshimizu T, Usami S, Fujimoto T. 1981. Toxicity of aspartame and its diketopiperazine for Wistar rats by dietary administration for 104 weeks. Toxicology 21:91–94. Kodell RL, Lin KK, Thorn BT, Chen JJ. 2000. Bioassays of 1441