Dose-response relationship in multistage carcinogenesis: promoters.

Published dose-response curves of promoters of multistage carcinogenesis were selected that met the combined criteria of long study times, multiple doses, and low doses. In rat liver, 12 dose-response studies of 7 different promoters (phenobarbital, 2,3,7,8-tetrachlorodibenzo-p-dioxin [TCDD], clophen A-50 (a polychlorinated biphenyl), alpha-, beta-, and gamma-hexachlorocyclohexane [HCH], and chloroform) were selected. These promoters were studied for 7-86 weeks and either altered hepatic foci or hepatic cancer were determined. The doses ranged from 1 ng (TCDD) to 400 mg (chloroform). In mouse skin, 10 dose-response studies of 4 promoters (12-O-tetradecanoylphorbol-13-acetate [TPA], anthralin, chrysarobin, and 2,6-di-tert-butyl-4-hydroperoxyl-2,5-cyclohexadienone [BHTOOH]) were selected. In these mouse skin studies the doses ranged from 0.425 nmole (TPA) to 20,000 nmole (BHTOOH) per mouse. The length of time promoters were applied to the skin varied between 15 and 60 weeks. Either skin papillomas or carcinomas were determined. The dose-response relationships are presented on the basis of moles of promoter, percentage of the fully effective promoting dose, or percentage of the acute oral rat LD50. The degree of concavity of the dose-response curves was determined. The available dose-response data are critiqued and discussed on the basis of future research needs for biologically based cancer risk assessment models.