Selective estrogen receptor modulators (SERMs) act exclusively through estrogen 
receptors and possess tissue-specific agonistic or antagonistic properties. The 
effects of all referred SERMs in bone and cardiovascular system are estrogenic, 
namely they inhibit postmenopausal bone loss and favorably influence plasma 
lipoproteins and some coagulation factors. The aim of this paper is to review 
the effects of SERMs on estrogen-dependent breast tissues and on the 
endometrium. There are two types of SERMs in clinical use, based on their 
chemical structure: the triphenylethylenes and the benzothiophenes. The 
prototype of the SERMs with triphenylethylene structure is tamoxifen. Tamoxifen, 
like all other SERMs, is an estrogen antagonist in the breast and is widely used 
for adjuvant treatment of breast cancer. A recent study suggests that tamoxifen 
also may prevent breast cancer in patients at risk. Because of the partial 
estrogenic activity of tamoxifen in the endometrium, its clinical use is 
associated with uterine hypertrophy and an increased risk of endometrial cancer. 
Other triphenylethylene SERMs, droloxifene, toremifene, and idoxifene, also show 
efficacy in the treatment of breast cancer, in a manner similar to tamoxifen. A 
better toxicology profile and a decreased endometrial estrogen agonism may be 
advantages of the new triphenylethylene SERMs. Raloxifene is a SERM with a 
chemical structure different from triphenylethylenes. Raloxifene, a 
benzothiophene, possesses an estrogen-antagonistic effect in the breast similar 
to triphenylethylenes. Clinical studies on postmenopausal osteoporotic women on 
raloxifene as compared with placebo show a significant decrease in the rate of 
newly diagnosed breast cancers. In clinical studies, in contrast to tamoxifen, 
no stimulatory effect in the endometrium could be observed with raloxifene.