Dose–Response Relationships in Chemical Carcinogenesis and Cancer Risk Assessment

I. INTRODUCTION A. Tumor Incidence in Animal Bioassays In a standard test for carcinogenicity of a chemical with 50 animals per dose group, an increase in tumor incidence must be about 10% to become statistically significant. For humans, a 10% lifetime cancer risk (1 in 10) would not be acceptable, unless the exposure is voluntary, such as by cigarette smoking. For most human cancer risk assessments, therefore, extrapolation to lower doses is necessary.