Hormonal dependency of experimental mammary tumors induced by an estro-progestational combination

Mammary tumours were induced in rats by administration of an estradiol-progesterone association. These tumours offered close analogies with human mammary tumours. The estradiol-receptor was found both in cytosol and nuclei and was more abundant in nuclei than in cytosol. The major part of its binding sites was occupied by endogenous hormone. On the other hand, a high level of progesterone receptor was present in tumoral cytosol. This fact gave evidence of the complete activity of the estradiol receptor. The presence of estradiol and progesterone receptors in mammary tumors induced by these hormones substantiate their hormone-dependence.