Mammary tumour development in BR6 mice: hormonal stimulation.

BR6 female mice treated with a mixture of hormones, developed mammary tumours earlier than untreated virgin animals. Implantation of ectopic pituitaries also increased tumour incidence and reduced the age at which tumours first appeared. This effect was obtained even in the absence of ovaries. Neither hormone treatment nor ectopic pituitaries succeeded in producing tumours as early as they appear in breeding females.