[Mammary tumors in female rats with combined exposure to nitrosoethylurea and sex hormones].

Transplacental treatment with sinestrol and testosterone-propionate reduces the incidence of spontaneous benign mammary tumors in rats. Treatment of immature female rats with nitrosoethylurea is followed by an earlier development of mammary fibroadenomas. A combined treatment with testosterone-propionate and nitrosoethylurea increases the incidence of mammary fibroadenoma and decreases its mean latent period. Fibroadenoma induction is accelerated by treating adult rats with nitrosoethylurea alone, while combined treatment induces primary mammary tumors at an earlier stage. The morphology of tumors induced by different schemes of combined treatment remains identical.