Age-Related Differences in Susceptibility to Carcinogenesis a Quantitative Analysis of Empirical Animal Bioassay Data
As part of its revision of cancer risk assessment guidelines, the U.S. Environmental Protection Agency has assembled and analyzed animal cancer bioassay data for exposures to mutagenic and putatively non-mutagenic chemicals over different periods of life. This paper reports an improved analysis of these data, supplemented with some chemical carcinogenesis data not included in the orginal analysis, and animal bioassay studies of ionizing radiation. We use likelihood methods to avoid excluding cases where no tumors were observed in either adult or other groups. We express dosage for animals of different weights on a metabolically consistent basis (either concentration in air or food, or per unit body weight to the three quarters power). Finally, we use a system of dummy variables to represent exposures during fetal, pre-weaning, and weaning-60 day postnatal periods -- yielding separate estimates of relative sensitivity per day of dosing in these intervals.