Carcinogenic Effects of Oral Diethylstilbestrol on C3H Male Mice With and Without the Mammary Tumor Virus

Diethylstilbestrol (DES), at 250 parts per billion, was administered in the diet to castrated C3H/An male mice (with the mammary tumor virus) and C3H/Anf male mice (presumably free of the virus). In experiment I, mice of both substralns were observed for mammary tumor formation during 18 months on either DES-containing or control (DES-free) diets; mice in experiment II were observed for 12 months. In groups on control diets, no mammary tumors were found in 80 C3H/An mice, and only 1 tumor was observed in 80 C3H/Anf mice. In groups receiving DES, tumor incidence was 45/80 for C3H/An and 5/80 for C3H/Anf mice. The experiments emphasized that estrogen stimulation of genetically susceptible mice without the mammary tumor virus is not efficient in producing mammary tumors, nor is the virus effective without estrogen.