Carcinogenicity study with technical-grade dichlorodiphenyltrichloroethane and 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene in hamsters.

Studies conducted by others have revealed that 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (DDE), a proximal metabolite of dichlorodiphenyltrichloroethane (DDT), is a strong hepatocellular carcinogen in mice. Since hamsters appear to be resistant to tumor induction by DDT, we wanted to investigate whether DDE has any neoplastic effect in this species. DDE (99% pure) was mixed into the diet at doses of 500 or 1000 ppm and given to groups of male and female Syrian golden hamsters for life. Another group of animals received a diet containing 1000 ppm technical-grade DDT, and a further group served as control. Groups contained a minimum of 40 hamsters per sex. The tested compounds had no effect on the incidence of tumors at all sites, compared to controls. A specific finding in animals exposed to DDE was the appearance of hepatocellular tumors late in life. They were classified as neoplastic nodules, and the incidence was 15% in females and 47% in males of the 500-ppm DDE dose groups and 21% in females and 33% in males of the 1000-ppm DDE dose groups. None of the untreated or DDT-treated animals had these tumors. Eight animals treated with 1000 ppm DDE and four of those treated with DDT had hyperplastic foci of the liver. In addition, adrenocortical adenomas, spontaneous to Syrian golden hamsters, were more frequent in DDE- and DDT-treated animals than in control animals. These results showing that DDE, but not its parental compound, induces liver cell tumors in hamsters emphasize the importance of this metabolite as a proximal carcinogen of DDT.