Effects of methoxychlor on skin tumor development

Organochlorine pesticides increase the incidence of liver cancer through a multistage process involving tumor promotion. Mirex, an organochlorine pesticide has been shown to be a tumor promoter in mouse skin. In the present study, the effects of methoxychlor, a commonly used organochlorine pesticide, on the development of papillomas in 7,12-dimethylbenz[a]anthracene (DMBA)-initiated mouse skin and induction of mouse epidermal ornithine decarboxylase (ODC) activity were investigated and compared with 12-O-tetradecanoylphorbol-13-acetate (TPA), a well-known tumor promoter. Methoxychlor neither caused tumor development nor induced epidermal ODC activity. However, TPA resulted in 100% tumor incidence and 8.8 tumors per mouse after 20 weeks of promotion, and induced epidermal ODC activity.