Faculty Bibliography

Tamoxifen, the first clinically available SERM, was developed in 1966 and approved by the FDA (United States Food and Drug Administration) in 1978. It is the most prescribed antineoplastic drug in the world, with approximately 10 million women-use-years of experience. Tamoxifen has proved efficacious in all settings of breast cancer. However, in the mid-to-late 1980s, a series of letters to the editor and case reports announced an association between tamoxifen therapy in women with breast cancer and the development of endometrial carcinoma. Subsequently, in 1998, the observation of a significant 49% reduction in invasive breast cancer relative to placebo in a cohort of women at increased risk for the disease resulted in the early stopping of the National Surgical Adjuvant Breast and Bowel Project's (NSABP) P-1: Breast Cancer Prevention Trial (BCPT). Importantly, this was the first time that information became available about the effects of tamoxifen in healthy women, that is, women who did not already have breast cancer. In this healthy population, the relative risk of developing endometrial carcinoma in the tamoxifen arm was 2.54, although when stratified by age, in women over 50, the risk grew to 4.01. Thus, the risk appears to be confined to women over 50 because, in contrast, in women under 50 there was no statistically significant increase in the risk of endometrial carcinoma

Selective oestrogen receptor modulators (SERMs) are structurally diverse non-steroidal compounds that bind to oestrogen receptors and produce oestrogen agonist effects in some tissues and oestrogen antagonist effects in others. SERMs are being evaluated for a number of oestrogen-related diseases, including post-menopausal osteoporosis, hormone-dependent cancers, and cardiovascular disease. Several compounds that exhibit a SERM profile are currently available for clinical use, including clomiphene, tamoxifen, and toremifene (which are triphenylethylenes) and raloxifene (a benzothiophene). Clomiphene is used for the induction of ovulation in sub-fertile women attempting pregnancy. Tamoxifen and toremifene are both used to treat breast cancer. Tamoxifen may have beneficial effects on bone mineral density and serum lipids. The effects of toremifene on serum lipids are similar to that of tamoxifen. Both compounds have stimulatory effects on the endometrium. Raloxifene, indicated for the treatment and prevention of post-menopausal osteoporosis, has beneficial effects on bone mineral density and serum lipids, but does not increase the risk of endometrial hyperplasia or endometrial cancer. Recently, raloxifene was shown to reduce the incidence of vertebral fractures in otherwise healthy women with osteoporosis; in the same study, a reduced incidence of breast cancer was also observed. Similar to oestrogens, SERMs increase the incidence of venous thromboembolism. Several newer compounds that exhibit a SERM profile are also in clinical development, including other triphenylethylenes (droloxifene, idoxifene) and benzothiophenes (LY353381.HCl), benzopyrans (EM-800), and naphthalenes (CP-336,156)

Tamoxifen was approved for breast cancer prevention in October 1998. Thus, for the first time, we as gynecologists are being asked to prescribe this drug to healthy women. In the past each one of us has cared for women with breast cancer who have been treated with tamoxifen by oncologists or breast surgeons for the malignancy. Effects of tamoxifen on the uterus resulting in carcinomas, hyperplasia, and polyps are well known. Furthermore, tamoxifen has estrogenic properties in the venous system, increasing the incidence of deep vein thrombosis and pulmonary emboli. A new SERM (selective estrogen receptor modulator), raloxifene, has been approved for prevention and treatment of osteoporosis in postmenopausal women. It does not have stimulatory effects on the endometrium; however, it is estrogenic in the venous system. Preclinical data, as well as the breast cancer incidence reported in studies of the skeleton, seem to indicate that its effects in the breast are similar to those of tamoxifen. This article reviews tamoxifen and the new SERM, raloxifene, in an attempt to help gynecologists better understand each compound and what data are currently known, what we hope to learn from future studies, and what currently makes sense for clinical practice

OBJECTIVE: To determine the effects of a selective estrogen receptor modulator, raloxifene, on postmenopausal endometrium. METHODS: Healthy postmenopausal women (n = 415) were randomly assigned to one of the following four groups: 60 or 150 mg/day raloxifene hydrochloride, 0.625 mg/day conjugated equine estrogens, or placebo, and treated for 1 year. Endometrial biopsies were obtained in a blinded fashion at baseline and every 6 months after the ultrasound studies. Transvaginal ultrasound, with uterine size measurements, was done at baseline and at 3-month intervals. Saline-infusion sonohysterography was done at baseline and every 6 months. RESULTS: There were no statistically significant differences in baseline characteristics. Mean endometrial thickness, measured by transvaginal ultrasound, was unchanged from baseline to end point in the placebo and raloxifene groups, whereas in the estrogen group it was significantly thicker by 5.5 mm (P < .001). Mean uterine volume, calculated from transvaginal ultrasound measurements, was higher in the estrogen group only (22 cm3, P < .001). Of the 358 women with paired biopsies, endometrial hyperplasia was present in 2.1%, 0%, and 26.1% of the end-point biopsies in the placebo, raloxifene, and estrogen groups, respectively (P < .001). Proliferative endometrium was present in 2.1% of the end-point biopsies in the placebo group, 1.7% in the combined raloxifene groups, and 39.8% in the estrogen group (P < .001). CONCLUSION: Raloxifene, at 60 or 150 mg/day for 1 year, did not stimulate the postmenopausal endometrium. End-point endometrial thickness, morphology, and uterine volume in the raloxifene groups were similar to those observed at baseline and in the placebo group

In the mid 1980s when tamoxifen was shown to be associated with endometrial neoplasia there was a renewed interest in another SERM compound, raloxifene. Experimental animal data suggested that raloxifene did not stimulate the endometrium as tamoxifen does while having similar anti-oestrogenic effects in breast tissue as tamoxifen. Clinical data has now shown that raloxifene does not stimulate the endometrium in postmenopausal women. It results in no hyperplasia, no increase in endometrium thickness or polyp formation and virtually no proliferation. Further studies are necessary to see if long-term raloxifene use will reduce the risk of endometrial cancer. In studies of raloxifene as treatment for osteoporosis, when viewed as a secondary endpoint there was a significant reduction in risk of new onset breast cancer. Further studies with breast cancer as a primary endpoint are ongoing (the STAR Trial)

Selective estrogen receptor modulators (SERMs) are a new category of therapeutic agents, which bind with high affinity to estrogen receptors and mimic the effect of estrogens in some tissues but act as estrogen antagonists in others. Tamoxifen, a triphenylethylene derivative, was the first clinically available SERM. It is a potent anti-estrogen in the breast, and its use in breast cancer patients has made it the most widely prescribed antineoplastic drug worldwide. It has estrogen-like activity on bone metabolism, as well as cholesterol reduction. However, its ability to produce proliferation, and polyp formation, and even carcinomas, in the endometrium is well known. A new SERM, raloxifene, a benzothiopene derivative, has a clinical profile similar to tamoxifen's. However, preclinical as well as clinical studies reveal that unlike tamoxifen it is a pure anti-estrogen in the uterus. It has recently been FDA approved for prevention of osteoporosis in postmenopausal women. This report reviews pertinent preclinical and currently available clinical studies about this new SERM and discusses clinical applicability