SERMs are developped in HRT in order to provide the beneficial effects of e
stradiol on bone and the cardiovascular system. SERMs are antiestrogens and
their properties depend upon the pharmacological class they belong to. Tib
olone is a progestin with mixed properties. Our studies on breast cells in
vitro demonstrated that it behaves as a progestin in these cells. The clini
cal data obtained with these various therapies on breast are presented.