Abstract
Experiments were undertaken to determine the effect of progesterone on mammary tumour development in rats adrenalectomized or adrenalectomized and ovariectomized 7 days before 7, 12-dimethylbenz(a)anthracene (DMBA) treatment.
It was found that adrenalectomy had no significant effect on mammary tumour induction by DMBA, and if, in addition, injections of progesterone were given, beginning 2 days before DMBA, mammary tumorigenesis was enhanced to approximately the same extent as that observed previously in entire animals. Combined adrenalectomy and ovariectomy completely inhibited mammary carcinogenesis even when, in addition, progesterone was continuously administered. It is concluded that the presence of at least a basal level of oestrogen appears to be essential for DMBA mammary tumorigenesis, and that while progesterone enhances the production of DMBA-induced mammary cancer in rats, it does not appear to be necessary for its induction.