There were no significant differences in mammary tumour incidence or multiplicity in comparison with controls that did not receive the metabolite. Other relevant data Oestrogens administered orally are absorbed rapidly and achieve maximum serum levels quickly. Some oestrogens, including conjugated oestrogens, have been reported to have genotoxic activity in experimental systems. At higher concentrations, which may or may not involve receptor mediation, oestrogens have been reported to induce changes in DNA and chromosomes. Oestradiol binds to oestrogen receptors with higher affinity than oestriol or oestrone.
Oestrogens can increase the number of proliferating cells in the human endometrium in vivo .
It has been reported that oestrogens increase cell proliferation in normal breast cells in monkeys and in cultured human breast cancer cells. At higher concentrations, oestrogens stimulated cell proliferation in rat liver in vivo and in cultured rat hepatocytes in vitro . No information was available on whether the effect of oestrogens on the mammary gland is modified by body weight or by the recency or duration of exposure to oestrogens in experimental systems. Similarly, no information was available on the possible relationship between exposure to oestrogens and the degree of malignancy of breast tumours. There is sufficient evidence in humans for the carcinogenicity of post-menopausal oestrogen therapy.