Combined endocrine effects of LHRH agonist (Zoladex) and tamoxifen (Nolvadex) therapy in premenopausal women with breast cancer

Estrogen levels in young women with hormone receptor-positive breast cancer on ovarian function suppression therapy

Ovarian function suppression (OFS) benefits young women with hormone receptor (HR)-positive breast cancer but they are at risk for ovarian function breakthrough. We assessed endocrine effects of gonadotropin-releasing hormone agonist (GnRHa) treatment in a prospective cohort of patients aged ≤ 40 years with HR-positive breast cancer. Plasma estradiol (E2), estrone, and follicule-stimulating hormone (FSH) levels were measured from blood samples drawn 1 and 4 years after diagnosis. Patient characteristics, invasive breast cancer-free survival (iBCFS), and overall survival (OS) were compared between those with and without E2 > 2.72 pg/mL during GnRHa treatment. Among eligible patients, 54.7% (46/84) and 60% (15/25) had E2 > 2.72 pg/mL at 1 and 4 years, respectively. Factors associated with E2 > 2.72 pg/mL at 1 year were no prior chemotherapy (P = 0.045) and tamoxifen use (P = 0.009). After a median follow-up of 7 years, among patients with stage I-III breast cancer (N = 74), iBCFS events were seen in 6 (8.1%) with E2 > 2.72 pg/mL and 5 (6.8%) with E2 ≤ 2.72 pg/mL (P = 0.893). Among patients with de novo metastatic breast cancer (N = 12), 6 (50%) with E2 > 2.72 pg/mL and 3 (25%) with E2 ≤ 2.72 pg/mL died during follow-up (P = 0.052). Larger studies exploring the clinical implications of incomplete E2 suppression by GnRHa are needed to ensure optimal OFS treatment strategies are being employed for this population.

Adjuvant ovarian suppression for premenopausal hormone receptor-positive breast cancer: A network meta-analysis

BACKGROUND

Ovarian function suppressor (OFS) plus either tamoxifen (TAM) or aromatase inhibitor (AI) could improve the survival outcome for premenopausal hormone receptor-positive (HR+) breast cancer. However, the optimal OFS-based regimen and medication duration remain uncertain. This article aims to systematically evaluate the OFS-based adjuvant endocrine therapy for premenopausal breast cancer.

METHODS

We searched several public databases from January 1980 to November 2020. A random model was adopted in this meta-analysis. We used the hazard ratio (HR) with a 95% confidence interval (CI) for the statistical analysis of efficacy. The primary outcome measures included overall survival and disease-free survival.

RESULTS

A total of 32 articles with 37,224 cases were included in this network meta-analysis. OFS+TAM improved 5-year disease-free survival (HR -0.09, 95% CI -0.16 to -0.01) and 5-year overall survival (HR -0.18, 95% CI -0.33 to -0.03) compared with TAM monotherapy. For OFS+AI, although the 5-year disease-free survival was improved (HR -0.18, 95% CI -0.29 to -0.08), the 5-year overall survival was not improved (HR -0.13, 95% CI -0.43 to 0.18). In subgroup analysis, both OFS+AI and OFS+TAM showed a protective effect in stage I-III patients compared with stage I-II patients. For the course of therapy, OFS+TAM for 2-years could achieve clinical benefit and the best course of therapy of OFS+AI still waits for further study.

CONCLUSIONS

OFS+TAM might be a better option than OFS+AI for premenopausal intensive adjuvant endocrine therapy. Stage III patients are more suitable for the OFS-based therapy. For the medication duration, the 2-years course of OFS+TAM could be effective. This analysis provides helpful information for selecting therapeutic regimen in intensive adjuvant endocrine therapy and identifying the target population.

Measuring Ovarian Escape in Premenopausal Estrogen Receptor-Positive Breast Cancer Patients on Ovarian Suppression Therapy

PURPOSE

This study evaluated the proportion of premenopausal women who experience persistent ovarian escape (OE) while receiving ovarian suppression (OS) therapy for estrogen receptor-positive (ER+) breast cancer treatment. The study also examined clinical factors that may predispose to higher risk of persistent OE.

MATERIALS AND METHODS

This was a retrospective, "real-world" study to evaluate premenopausal women receiving adjuvant endocrine OS therapy. The primary objective was to measure the percentage of persistent OE within the first 3 months of OS injections (using either leuprolide or goserelin). The secondary objective was to associate baseline clinical data (age, body mass index [BMI], and previous chemotherapy) with the probability of OE.

RESULTS

Of the 46 patients included in this analysis, 11 (23.9%) women did not achieve OS within 3 months. Three women (6.5%) remained in OE at 12 months. Older age (odds ratio, 0.86; confidence interval, 0.76-0.98, p = .024) was associated with lower chance of developing OE. BMI, previous chemotherapy, and drug used (tamoxifen versus aromatase inhibitor) did not correlate with the likelihood of OE in this patient cohort.

CONCLUSION

Among the premenopausal women who did not attain complete ovarian suppression, young age was a significant risk factor for likelihood of OE. Although the clinical relevance of this finding is not yet known, it should prompt further studies to determine whether inadequate OS is associated with higher recurrence risk for patients with ER+ breast cancer.

IMPLICATIONS FOR PRACTICE

Because up to a quarter of premenopausal women do not attain adequate ovarian suppression within the first 3 months of gonadotropin-releasing hormone (GnRH) agonist therapy, bloodwork should be checked to ascertain hormone levels prior to starting aromatase inhibitor therapy, and at regular intervals, for these women.

Spotlight on triptorelin in the treatment of premenopausal women with early-stage breast cancer

Endocrine treatment represents the cornerstone of endocrine-sensitive premenopausal early breast cancer. The estrogen blockade plays a leading role in the therapeutic management of hormone receptor-positive breast cancer together with surgery, radiotherapy, and selective antiestrogen treatments. For several years, selective estrogen receptor modulators, such as tamoxifen, have represented the mainstay of therapy. The role of amenorrhea has been extensively elucidated in the past year: the benefit observed with chemotherapy-induced amenorrhea has strengthened its therapeutic role. Luteinizing hormone-releasing hormone (LHRH) has been introduced in oncology practice to induce amenorrhea in order to increase the advantage obtained from endocrine treatment. Triptorelin is one of the most widely used LHRH analogs currently available in clinical practice. It was recently investigated in two major clinical trials that studied the role of complete estrogen blockade in the premenopausal setting. Both showed the clinical benefit due to ovarian suppression treatment, primarily in high-risk patients. Furthermore, triptorelin and other LHRH analogs have recently been investigated in the attempt to preserve the ovarian function in young patients. The medical treatment of early breast cancer is always evolving in the effort to search for safe and efficacious treatments. The role of LHRH analogs is actually well recognized as contributing to the improvement of the medical treatment of premenopausal women with early breast cancer.

Adjuvant goserelin and ovarian preservation in chemotherapy treated patients with early breast cancer: results from a randomized trial

The purpose of this randomized study was to examine if goserelin concomitant to CMF-chemotherapy as adjuvant treatment for premenopausal breast cancer, protects the ovaries from premature failure. A total of 285 premenopausal breast cancer patients, in a randomized adjuvant trial (Zoladex in premenopausal patients (ZIPP)), were assigned to a study on ovarian function. Node positive patients were assigned to CMF-(cyclophosphamide, methotrexate and 5-fluorouracil) chemotherapy in addition to endocrine therapy. All patients were randomly assigned to receive 2 years of goserelin, goserelin plus tamoxifen, tamoxifen alone or no endocrine treatment. We studied, if menses were affected in the treatment groups, up to 36 months after randomization. One year after completed CMF- and endocrine therapy, 36% of the women in the goserelin group reported menses, compared to 7% in the goserelin plus tamoxifen group, 13% in the tamoxifen group and 10% of the controls. Among women treated with goserelin, there was a statistically significant increase in the proportion of menstruating women, 1 year after completed treatment compared to at 24 months of treatment (P = 0.006), in contrast to all other treatment groups, who were unchanged or more often amenorrheic. In our study, there is some evidence of protective effect of goserelin on ovarian function in CMF treated women. This effect was not observed in the combined tamoxifen and goserelin treatment.

Endocrine therapy for breast cancer: an overview

Endocrine therapy for breast cancer has been established in the adjuvant treatment for primary disease and in the treatment of advanced disease. The ER remains the best predictor of response although other factors exist and need to be identified. Pharmacological manipulation has been replacing ablative procedures. Tamoxifen used to be the most popular agent of choice and promising new agents include the pure anti-oestrogens and the third generation selective aromatase inhibitors. Ongoing and future studies will optimise treatment in established areas and will exploit its potential roles in preoperative use and chemoprevention.

Clinical and endocrine data for goserelin plus anastrozole as second-line endocrine therapy for premenopausal advanced breast cancer

A total of 16 premenopausal women with metastatic breast cancer (N=13) or locally advanced primary breast cancer (N=3) were treated with a combination of a gonadotropin-releasing hormone agonist goserelin, and a selective aromatase inhibitor anastrozole. All had previously been treated with goserelin and tamoxifen. In all, 12 patients (75%) achieved objective response or durable stable disease at 6 months, with a median duration of remission of 17+ months (range 6–47 months). Four patients still have clinical benefit. Introduction of goserelin and tamoxifen resulted in an 89% reduction in mean oestradiol levels (pretreatment vs 6 months=224 vs 24 pmol l⁻¹) (P<0.0001). Substitution of tamoxifen by anastrozole on progression resulted in a further 76% fall (to 6 pmol l⁻¹ at 3 months) (P<0.0001). Treatment with goserelin and tamoxifen led to a 90% fall in the mean follicle-stimulating hormone (P<0.001). This was reversed once therapy was changed to goserelin and anastrozole. A similar initial reduction was seen in the mean luteinising hormone levels, but substitution of tamoxifen by anastrozole on progression resulted in no significant change. Goserelin and tamoxifen did not lead to any significant change in testosterone and androstenedione levels. The combined use of goserelin and anastrozole as second-line endocrine therapy produces a significant clinical response of worthwhile duration, with demonstrable endocrine changes, in premenopausal women with advanced breast cancer, and offers them another therapeutic option. Further studies involving more patients and longer follow-up are indicated.

The use of gonadotrophin-releasing hormone (GnRH) agonists in early and advanced breast cancer in pre- and perimenopausal women

Gonadotrophin-releasing hormone (GnRH) agonists, in particular goserelin ('Zoladex'), are increasingly being used for the treatment of breast cancer in women with functioning ovaries. They act by downregulating pituitary GnRH receptors, thereby suppressing the release of luteinising hormone (LH) and follicle stimulating hormone (FSH), which, in turn, reduce the main source of oestradiol production in the ovaries. GnRH agonists have been shown to be as effective therapeutically as surgical ovarian ablation in pre- and perimenopausal women with advanced breast cancer. The combination of a GnRH agonist such as goserelin with the peripheral oestrogen antagonist, tamoxifen, may be used to produce 'combined oestrogen blockade'. In advanced breast cancer, this regimen prolongs progression-free survival and increases both the response rate and duration relative to the use of a GnRH agonist alone. In patients with early breast cancer, the addition of goserelin to 'standard treatment' (i.e. surgery+/-tamoxifen, chemotherapy or radiotherapy) results in a significant benefit in recurrence-free survival and overall survival. This benefit was most apparent in patients with oestrogen receptor (ER) +ve tumours. Goserelin, when used either alone or in combination with tamoxifen as an adjuvant systemic therapy in women with ER +ve tumours, has been shown in clinical trials to produce recurrence-free survival rates equivalent to cytotoxic chemotherapy such as cyclophosphamide, methotrexate, 5-fluorouracil (CMF). Evidence suggests that at least part of the effect of adjuvant cytotoxic chemotherapy in premenopausal women is produced by ovarian ablation. Endocrine therapy with goserelin or goserelin plus tamoxifen should now be considered a treatment option in the management of premenopausal women with ER +ve early breast cancer.

Methods of ovarian suppression used in the UK

Ovarian suppression in the management of breast cancer has had a resurgence in the 1990s. In view of the development of luteinizing hormone-releasing hormone (LHRH) analogues and advances in laparoscopic surgery, we wished to determine whether more consultants are considering these methods for achieving ovarian suppression than radiotherapy. A questionnaire was designed to determine the current practice of consultants in the UK and to discover who is involved in making this decision. It was distributed via the Adjuvant Breast Cancer (ABC) trials office to consultants who enter patients into the ABC premenopausal trial. Seventy-four (72%) questionnaires were analysed. The preferred method of treatment was radiotherapy in 60%, surgery in 30% and LHRH analogues in 9%. Seventy-three per cent of consultants were using more than one technique but did not always involve the patient in the decision-making process to determine which treatment modality to use. Radiotherapy techniques used included using bony landmarks for field borders (46%), using a standard field size (20%) or using ultrasound localization (15%).

Combination endocrine therapy in the management of breast cancer

Combination endocrine therapy has long been sought after as a means to better treat breast cancer. Agents that suppress estrogen production are given with agents that suppress estrogenic activity at the cellular level. Historically, these combinations have resulted in initial improvements in response rates, but relapse-free and overall survival were not significantly improved. Also, the increased toxicity seen with these regimens was limiting. New endocrine therapies with more potent activity and less toxicity have led to a resurgence of this idea in the management of breast cancer. Complete estrogen blockade has been compared with single-agent treatments in many different settings. The endocrine effects of this type of therapy are intriguing, but apparently do not readily predict a clinical advantage. The combination of an aromatase inhibitor and an antiestrogen, despite pharmacokinetic interactions, may prove to be beneficial. Results from ongoing trials are eagerly awaited to further address this question in postmenopausal breast cancer patients. For premenopausal breast cancer patients the options are more complex. Clinical outcomes with leutinizing hormone releasing hormone (LHRH) agonists plus aromatase inhibitors are limited to very small phase II studies and are not clearly superior to single-agent therapy. Clinical data in the metastatic setting with premenopausal patients favor the use of an LHRH agonist with tamoxifen over the use of an LHRH agonist alone. However, a similar comparison with tamoxifen alone is lacking with only one trial including this as a treatment arm. Adjuvant therapy with this combined endocrine approach (LHRH agonist plus antiestrogen) has been more extensively studied, but lacks crucial comparisons necessary for making complex treatment decisions. Hopefully, through investigative diligence and ingenuity this issue can be adequately understood. However, many exciting new agents are on the horizon that offer hope to further advance the progress made to date although further confounding the questions already answered.

Combined tamoxifen and luteinizing hormone-releasing hormone (LHRH) agonist versus LHRH agonist alone in premenopausal advanced breast cancer: a meta-analysis of four randomized trials

PURPOSE

The logic behind the application of luteinizing hormone-releasing hormone (LHRH) agonists in combination with tamoxifen in premenopausal women is that LHRH agonists on the one hand suppress the tamoxifen-induced stimulation of the pituitary-ovarian function and, on the other hand, seem as effective as surgical castration. This meta-analysis combines all randomized evidence to compare the combined treatment with LHRH agonist alone with respect to overall survival, progression-free survival, and objective response in premenopausal women with advanced breast cancer.

PATIENTS AND METHODS

Four clinical trials randomizing a total of 506 premenopausal women with advanced breast cancer to LHRH agonist alone or to the combined treatment of LHRH agonist plus tamoxifen were identified. Meta-analytic techniques were used to analyze individual patient data from these trials.

RESULTS

With a median follow-up of 6.8 years, there was a significant survival benefit (stratified log-rank test, P = .02; hazards ratio [HR] = 0.78) and progression-free survival benefit (stratified log-rank test, P = .0003; HR = 0.70) in favor of the combined treatment. The overall response rate was significantly higher on combined endocrine treatment (stratified Mantel Haenszel test, P = .03; odds ratio = 0.67).

CONCLUSION

The combination of LHRH agonist plus tamoxifen is superior to LHRH agonist alone in premenopausal women with advanced breast cancer. Therefore, if a premenopausal woman with advanced breast cancer is thought to be suitable for endocrine treatment, it is proposed that the combination of a LHRH agonist plus tamoxifen be considered as the new standard treatment.

The Role of Hormonal Therapy in Breast Cancer

This review reassesses the role of hormonal therapy in breast cancer specifically the sequential or concurrent use of endocrine therapy and the combined use of chemotherapy with endocrine therapy. In advanced disease the sequential use of hormone therapies is generally recommended rather than the combined use of various hormonal agents, though combination hormonal therapy offers advantages in certain subsets of patients. The efficacy of combined chemo-endocrine therapy is questionable. Chemotherapy with estrogenic recruitment is an attractive but still experimental concept. However, in an adjuvant setting there is evidence that combined chemo-endocrine therapy causes a significant increase in disease-free and/or overall survival, particularly in postmenopausal patients with estrogen receptor(ER)-positive tumors. While hormonal treatment strategies have clearly benefitted from randomized studies, data regarding optimal endocrine therapy are still insufficient.

Laparoscopic oophorectomy: a prospective evaluation in pre-menopausal breast cancer with particular reference to incidence and severity of menopausal symptoms

Laparoscopic oophorectomy offers potential advantages over other methods of ovarian ablation. In this prospective study the technique, complications and side-effects have been assessed in 69 consecutive patients. Menopausal symptoms were assessed using two scoring systems - the Kupperman index and the Women's Health Questionnaire. The serum beta oestradiol levels fell rapidly post-operatively (from 540 pmol/l to 25 pmol/l within 1 month). Menopausal symptoms were mild in 75% of patients and severe in none. Complications occurred in three patients. Laparoscopic oophorectomy has an important role to play in the management of pre-menopausal breast cancer and this study confirms that is well tolerated and gives good short-term results.

Clinical uses of antiestrogens

An antiestrogen is a compound that blocks the action of estrogen. Most synthetic antiestrogens have agonistic or antagonistic activity depending on the tissue and the endogenous estrogen mileu. The triphenylethylene derivatives, clomiphene and tamoxifen, are the antiestrogens in greatest clinical use. Their biologic effects, clinical indications, and risks are reviewed. Novel antiestrogens which are beginning to be studied clinically include the benzothiophene derivative, raloxifene and the "pure" antiestrogens such as ICI 182,780. New clinical indications for existing compounds as well as the development of novel antiestrogens may lead to better treatment options for endocrine-dependent conditions.

A randomised study to compare the effect of the luteinising hormone releasing hormone (LHRH) analogue goserelin with or without tamoxifen in pre- and perimenopausal patients with advanced breast cancer

The use of goserelin with or without tamoxifen was investigated in a randomised multicentre study involving 318 pre- and perimenopausal advanced breast cancer patients. With a median follow-up of 93 weeks, 31% of goserelin-treated patients had objective responses (UICC criteria) compared with 38% of goserelin plus tamoxifen-treated patients (P = 0.24). There was a modest benefit in favour of combination therapy in time to progression (P = 0.03) but not in survival (P = 0.25). Median follow-up for survival was 117.5 weeks. Median times for disease progression and survival were 23 and 127 weeks in the goserelin alone group and 28 and 140 weeks in the combination group, respectively. In 115 patients with skeletal metastases only, significant differences in favour of combination therapy were seen in response rate, time to progression and survival. Both treatments were well tolerated and no additional safety issues were associated with combination therapy.

Ovarian ablation versus goserelin with or without tamoxifen in pre-perimenopausal patients with advanced breast cancer: results of a multicentric Italian study

BACKGROUND

Oophorectomy is one of the treatments of choice for premenopausal women with advanced breast cancer. However, in recent years LH-RH analogs have replaced surgical castration (or ovarian irradiation) on the basis of the comparable therapeutic activity shown by these drugs in phase II studies. Moreover, the combination of tamoxifen and LH-RH analogs has gained popularity among clinicians attempting to obtain a 'total estrogen blockade' according to the same rationale previously proposed for advanced prostatic cancer. However, it has thus far not been proven that medical castration is as effective as oophorectomy or ovarian irradiation, nor is there enough evidence that tamoxifen could improve the efficacy of ovarian ablation.

PATIENTS AND METHODS

Eighty-five perimenopausal patients with estrogen receptor or unknown positive metastatic breast cancer were randomly allocated to receive one of the following treatments: surgical castration (or ovarian irradiation); goserelin; surgical castration (or ovarian irradiation) plus tamoxifen; goserelin plus tamoxifen. The study was performed according to a 2 x 2 factorial randomised design.

RESULTS

While overall there was no significant difference in the response rates observed after two by two grouping, a trend did favour oophorectomy (or ovarian ablation) with respect to treatment activity. In fact, the best response rate was observed in patients allocated to this treatment (46.6% OR -95% CL: 21.2-72.9) while the lowest rate was observed in patients treated with oophorectomy plus tamoxifen (11.1% OR: CL: -3.4-25.6). Response to goserelin and goserelin plus tamoxifen was 27.2% (+/- 18.6) and 45% (+/- 21.8), respectively. Logistical regression analysis suggested that there might be a different interaction between tamoxifen and goserelin or oophorectomy (ovarian irradiation), respectively. Nevertheless, patient survivals were comparable, irrespective of allocated treatment. This indicates that two by two grouping has some value with respect to treatment efficacy and shows that oophorectomy (or ovarian irradiation) and goserelin have comparable efficacies. Tamoxifen did not improve the efficacy of gonadal ablation, although it did enhance the activity of goserelin treatment.

CONCLUSIONS

The results of the present study confirm prospectively that the efficacy of chemical castration is comparable to that of oophorectomy (or ovarian irradiation). The concurrent use of tamoxifen can probably enhance the activity of goserelin, but it also induces more side effects. However, it doesn't appear that 'total estrogen blockade' is more effective than gonadal ablation alone. Indeed, the question of whether chemical and surgical castration have the same effect in breast cancer is still open as is the one concerning the interaction between tamoxifen and gonadal ablation. Both questions should be addressed by prospective studies.

Reversible control of oestradiol-stimulated growth of MCF-7 tumours by tamoxifen in the athymic mouse

We investigated the ability of high concentrations of oestradiol to reverse the growth inhibitory action of tamoxifen on MCF-7 breast cancer cells in vivo. Tamoxifen inhibits the oestradiol stimulated growth of MCF-7 cells in athymic mice. Using a sustained release preparation of tamoxifen we consistently achieved serum concentrations of the drug in the 40 to 50 ng ml-1 range and much higher levels in tissues. These serum levels are sufficient to inhibit the oestrogen stimulated growth of MCF-7 tumours exposed to physiologic (i.e. 300-600 pg ml-1 serum oestradiol concentrations). However, by administering dosages that increase serum oestradiol concentrations to 900-2000 pg ml-1, mimicking the increase often observed clinically in premenopausal women taking tamoxifen, we show that the growth inhibitory action of tamoxifen can be partially reversed. Serum tamoxifen levels were elevated to nearly 400 ng ml-1 by injecting 1 mg day-1 tamoxifen (IP 3 x weekly); this dosage was more effective at inhibiting oestradiol stimulated tumour growth than subcutaneous tamoxifen capsules alone. Our data suggest that at low serum levels tamoxifen may not act optimally. There may be a need to monitor tamoxifen levels in premenopausal patients to ensure that they are high enough not to be overcome by a tamoxifen induced increase in ovarian steroidogenesis.

Goserelin (Zoladex) in premenopausal advanced breast cancer: duration of response and survival

In premenopausal women with advanced breast cancer the luteinising hormone-releasing hormone agonist goserelin (Zoladex, ICI plc) will produce serum levels of oestradiol equivalent to those following surgical oophorectomy or the menopause. This paper reports our further experience of using this drug in 75 premenopausal patients with advanced breast cancer. In addition to response rates, duration of response is reported. An objective response was seen in 25 patients (33%), the median duration of which was in excess of 15 months. Seven patients (9%) showed a complete response to therapy; median duration greater than 37 months. There was no significant difference in time to disease progression (Lee-Desu statistic 18.26, 1 d.f., P = 0.43) and probability of survival (Lee-Desu statistic 3.41, 1 d.f., P = 0.07) between those patients assessed as having either static disease, or those showing a partial response at six months. Response to therapy correlates significantly with the oestrogen receptor status of the primary tumour (X2 = 20.59, 6 d.f., P less than 0.005). The modest side-effects, ease of administration and reversibility make this approach to therapy very attractive. This is to be remembered in that 53% of patients had disease progression whilst receiving goserelin. These patients thus avoided the unnecessary and irreversible morbidity associated with surgical oophorectomy. With the proven efficacy and minimal morbidity associated with goserelin we believe there is no current role for surgical oophorectomy in the management of premenopausal patients with advanced breast cancer.

Estrogen deprivation in breast cancer. Clinical, experimental, and biological aspects

The endocrinological and clinical effects of an LH-RH agonist, Zoladex, and an antiestrogen, Nolvadex, in patients with advanced breast cancer are outlined and their potential in the therapy of nonmalignant diseases of the breast and high-risk states is briefly discussed. Additional data are presented to indicate that new antiestrogens are now available for experimental studies that, unlike tamoxifen, do not possess partial estrogen-like activity and that show favorable antitumor properties against DMBA-induced mammary tumors and MCF-7 human breast cancer cells in culture. The lack of agonistic effects of this new class of pharmacological agents now allows a state of total estrogen deprivation to be approached, a previously unobtainable clinical goal.