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IV.
DERIVATION OF CANCER POTENCY
Basis for Cancer Potency
Gold et al. (1984, 1987) list results from drinking water studies in male and female Syrian Golden
hamsters, feeding studies in male ICR mice, feeding studies in rhesus and cynomolgus monkeys,
intraperitoneal studies in rhesus monkeys (combined data for males and females), and drinking water
studies in Sprague-Dawley rats (combined data for males and females). N-Nitrosopiperidine induced
liver tumors in all species and strains. Hamsters are the least sensitive of the species tested. The
majority of treated primates developed liver tumors, including all cynomolgus monkeys given the
compound in feed. Rats and mice exhibit sensitivity similar to primates. Because treatment groups in
the primate studies are small and incidences observed are high, accurate estimates of cancer potency
cannot be obtained from these studies. Of the dose-response data available for rats and mice, the
highest quality data set is reported by Eisenbrand et al. (1980) for liver tumors in Sprague-Dawley rats.
Cancer potency is derived from this data set (Table 2) (Cal/EPA, 1992).
Methodology
Expedited Proposition 65 methodology (with cross-route extrapolation) was used to derive a cancer
potency factor. Analysis of the data set using the computer program TOX_RISK (Crump et al., 1991)
indicated that inclusion of the high dose group resulted in a p-value of = 0.05 based on the chi-square
goodness-of-fit test, indicating non-linearity. Following procedures described by US EPA (Anderson
et al., 1983), the high dose group was excluded from the analysis to correct for the poor fit (Cal/EPA,
1992). A unit risk factor of 6.0 E-6 (µg/m 3 ) -1 was derived by OEHHA/ATES from the human q 1 * using
an inspiration rate of 20 m 3 /day.
V. REFERENCES
Adamson RH and Sieber SM. 1982. Chemical carcinogenesis studies in nonhuman primates. In: Basic
Life Sciences, Vol. 24. Langenbach R, Nesnow S and Rice JM eds., Plenum Press, New York, pp.
129-156.
Anderson EL and the Carcinogen Assessment Group of the U.S. Environmental Protection Agency
1983. Quantitative approaches in use to assess cancer risk. Risk Anal. 3:277-295.
California Environmental Protection Agency (Cal/EPA) 1992. Expedited Cancer Potency Values and
Proposed Regulatory Levels for Certain Proposition 65 Carcinogens. Office of Environmental Health
Hazard Assessment, Reproductive and Cancer Hazard Assessment Section, Berkeley, CA.
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