Duration of remission to ICI 182,780 compared to megestrol acetate in tamoxifen resistant breast cancer

Fulvestrant for the treatment of advanced breast cancer

INTRODUCTION

The current issues with endocrine therapy for treatment of advanced breast cancer include balance of efficacy of therapy versus tolerability as well as hormone resistance. The efficacy of fulvestrant, a selective oestrogen receptor degrader (SERD), has been demonstrated in hormone receptor positive patients previously untreated or treated with hormonal therapy. Areas covered: This article discusses the journey of fulvestrant licensing, its efficacy in combination with other endocrine therapies and the future role it may have within breast cancer treatment. Expert commentary: Within phase III trials, fulvestrant has demonstrated equivalent or improved clinical efficacy when compared with established endocrine agents. In the recent decade, fulvestrant has achieved licensing as a second line agent in non-operative advanced breast cancer at initially 250mg, increasing to 500mg. Presently, fulvestrant is licensed globally as first line endocrine management for advanced breast cancer in post-menopausal women. Early combination trials of fulvestrant and cyclin dependent kinase 4/6 inhibitors have demonstrated good clinical efficacy with improved progression free survival when compared to fulvestrant alone.

Role of fulvestrant in the management of postmenopausal breast cancer

Fulvestrant is a form of endocrine therapy used in the treatment of postmenopausal breast cancer. It has a unique mechanism of action in that it causes the degradation of estrogen receptor and therefore has been labeled a selective estrogen receptor downregulator. Unlike the selective estrogen receptor modulator tamoxifen, it has no agonistic properties and is therefore a pure anti-estrogen. Given its low level of bioavailability and presystemic metabolism, it has been formulated as an intramuscular injection. A number of dosing regimens have been utilized - these include a dose of 250 mg monthly ('approved dose'), an initial 500 mg followed by 250 mg on days 14 and 28, and thereafter 250 mg every 28 days ('loading dose'), or 500 mg on days 0, 14 and 28, and thereafter every 28 days ('high dose'). This article will review its unique mode of action and preclinical data, as well as clinical data for different dosing regimens and data for its combination with aromatase inhibitors. Fulvestrant is a well-tolerated drug and its toxicities will also be reviewed. The optimal position of fulvestrant in sequential endocrine therapy has yet to be defined.

Fulvestrant in the management of postmenopausal women with advanced, endocrine-responsive breast cancer

Fulvestrant is a pure estrogen antagonist that binds, blocks and downgrades the estrogen receptor (ER). Its unique mechanism of action is its antitumor activity after progression on prior endocrine therapy. Fulvestrant has shown activity in ER-dependent cells that are ligand independent. Fulvestrant has been approved at 250 mg/month for postmenopausal women with hormone-sensitive advanced breast cancer after progression or recurrence on antiestrogen therapy. The fulvestrant 500 mg regimen has just received approval by the EMA and the US FDA, supported by dose-dependent ER downregulation and the recent results of the clinical trial CONFIRM. Fulvestrant in combination with systemic lowering of estrogen has shown no improvement over fulvestrant alone. Combination therapy with inhibitors of growth factor signaling may have greater efficacy and is under exploration. To enhance the benefit of fulvestrant and improve outcomes for individuals with ER-positive breast cancer, greater understanding of resistance mechanisms is required. A key issue is identification of patients with ER-positive disease who retain sensitivity to antiestrogen therapy after progression on tamoxifen and/or aromatase inhibitors.

Effectiveness and Tolerability of Fulvestrant in Postmenopausal Women with Hormone Receptor—Positive Breast Cancer

Fulvestrant, an estrogen receptor antagonist that downregulates the estrogen receptor but has no known agonist effects, has been evaluated in 2 randomized trials involving postmenopausal women with hormone receptor-positive, progressive advanced-stage breast cancer after disease progression with antiestrogen therapy. These phase III studies, from which data were reported separately and in a planned combined analysis, showed that fulvestrant 250 mg per month intramuscularly was at least as effective as anastrozole 1 mg per day orally with respect to the primary endpoint of time to progression as well as secondary efficacy endpoints, which included objective response, clinical benefit, and survival. Both trials showed that patients treated with fulvestrant had a significantly longer duration of response, and a retrospective analysis found that pretreatment with fulvestrant did not preclude response to third-line hormonal therapy. More recently, fulvestrant was shown to be active as first-line hormonal therapy for advanced-stage breast cancer, with overall efficacy similar to that of tamoxifen in patients with hormone receptor-positive disease. Fulvestrant has been well tolerated in comparative trials published to date, translating into low study withdrawal rates and maintenance of quality of life. The incidence of adverse events was similar between the treatment arms in both trials of fulvestrant versus anastrozole, but it was notably lower for fulvestrant relative to tamoxifen in the first-line setting. In light of the results of comparative phase III trials, fulvestrant is effective and well tolerated in the treatment of postmenopausal women with hormone receptor-positive advanced-stage breast cancer.

Challenges in the endocrine management of breast cancer

The goal of endocrine therapy in breast cancer is to block the action of estrogen on the tumor cells either by inhibiting estrogen from binding to the specific estrogen receptor or by inhibiting its synthesis. Tamoxifen, a selective estrogen receptor modulator, is the standard endocrine treatment for hormone receptor-positive breast cancer, both in the adjuvant and metastatic settings. Tamoxifen inhibits the binding of estrogen to the receptor, resulting in inhibition of hormone action. However, as tamoxifen is also weakly estrogenic, it may not be optimally effective and increases the risk of endometrial cancer and stroke. Furthermore, patients may be refractory or may become resistant to tamoxifen treatment. Since aromatase inhibitors (AI) block the synthesis of estrogen and have no intrinsic estrogenic activity, they have the potential to be more effective than tamoxifen. Their different mechanism of action and chemical structures may also circumvent tamoxifen resistance. Consequently, AIs are currently being evaluated as an alternative to tamoxifen treatment. A preclinical model has recently been developed to compare the efficacy of AIs and antiestrogens in different treatment schemes and to assist in the design of clinical trials. Current studies with the MCF-7Ca xenograft model are exploring the effects of combination and sequential therapy on tumor growth. The efficacy of AIs in the treatment of hormone receptor-positive breast cancer was first demonstrated in five multicenter second-line trials enrolling several hundreds of postmenopausal patients with metastatic breast cancer who had failed tamoxifen treatment. More recently, anastrozole demonstrated efficacy at least equivalent to that of tamoxifen in first-line randomized, phase III clinical trials in postmenopausal women with hormone receptor-positive or unknown metastatic breast cancer, whereas letrozole demonstrated superiority. The steroidal AI exemestane is currently under evaluation. Letrozole is the only AI to have been studied in a randomized, phase III trial in the neoadjuvant setting. In this trial, more patients underwent breast-conserving surgery with letrozole than with tamoxifen. Smaller phase II studies also suggest that both anastrozole and exemestane are active in the neoadjuvant setting. Because neoadjuvant trials permit temporal sampling of breast tissue, substudies in the phase III trial with letrozole have examined the impact of such biomarkers as estrogen receptor, progesterone receptor and epidermal growth factor receptor family members, HER-1 and HER-2, on patient response. AIs are currently under evaluation in the adjuvant setting, and preliminary results of the Arimidex, Tamoxifen Alone or in Combination (ATAC) trial have been reported. AIs have proven as safe as tamoxifen in trials in patients with metastatic breast cancer. Ongoing clinical trials in the adjuvant setting include companion studies of end-organ effects, particularly bone metabolism and lipid metabolism evaluations. Quality-of-life assessments are also parts of major clinical trials. A head-to-head quality-of-life assessment of anastrozole compared with letrozole demonstrated patient preference for letrozole. These assessments also clearly indicated the eagerness of patients to participate actively in treatment decisions

Fulvestrant, formerly ICI 182,780, is as effective as anastrozole in postmenopausal women with advanced breast cancer progressing after prior endocrine treatment

PURPOSE

To compare the efficacy and tolerability of fulvestrant (formerly ICI 182,780) and anastrozole in postmenopausal women with advanced breast cancer progressing after prior endocrine treatment.

PATIENTS AND METHODS

Patients (n = 451) with advanced breast cancer were randomized to receive fulvestrant 250 mg as a once-monthly (one x 5 mL) intramuscular injection or an oral dose of anastrozole 1 mg in this open, parallel-group, multicenter trial. The primary end point was time to progression (TTP). Secondary end points included objective response (OR) rates, defined as complete response (CR) or partial response (PR), duration of response (DOR), and tolerability.

RESULTS

Patients were followed for a median period of 14.4 months. In terms of TTP, fulvestrant was as effective as anastrozole (hazard ratio, 0.98; confidence interval [CI], 0.80 to 1.21; P =.84). Median TTP was 5.5 months for fulvestrant and 5.1 months for anastrozole. OR rates showed a numerical advantage for fulvestrant (20.7%) over anastrozole (15.7%) (odds ratio, 1.38; CI, 0.84 to 2.29; P =.20). Clinical benefit rates (CR + PR + stable disease > or = 24 weeks) were 44.6% for fulvestrant and 45.0% for anastrozole. Median DOR was 14.3 months for fulvestrant and 14.0 months for anastrozole. Both treatments were well tolerated, with 3.2% and 1.3% of fulvestrant- and anastrozole-treated patients, respectively, withdrawn from treatment because of an adverse event.

CONCLUSION

Fulvestrant was as effective as anastrozole. These data confirm that fulvestrant is an additional, effective, and well-tolerated treatment for advanced breast cancer in postmenopausal women whose disease progressed on prior endocrine therapy.

Double-blind, randomized trial comparing the efficacy and tolerability of fulvestrant versus anastrozole in postmenopausal women with advanced breast cancer progressing on prior endocrine therapy: results of a North American trial

PURPOSE

To compare the efficacy and tolerability of fulvestrant (formerly ICI 182,780) with anastrozole in the treatment of advanced breast cancer in patients whose disease progresses on prior endocrine treatment.

PATIENTS AND METHODS

In this double-blind, double-dummy, parallel-group study, postmenopausal patients were randomized to receive either an intramuscular injection of fulvestrant 250 mg once monthly or a daily oral dose of anastrozole 1 mg. The primary end point was time to progression (TTP). Secondary end points included objective response (OR) rate, duration of response (DOR), and tolerability.

RESULTS

Patients (n = 400) were followed for a median period of 16.8 months. Fulvestrant was as effective as anastrozole in terms of TTP (hazard ratio, 0.92; 95.14% confidence interval [CI], 0.74 to 1.14; P =.43); median TTP was 5.4 months with fulvestrant and 3.4 months with anastrozole. OR rates were 17.5% with both treatments. Clinical benefit rates (complete response + partial response + stable disease > or = 24 weeks) were 42.2% for fulvestrant and 36.1% for anastrozole (95% CI, -4.00% to 16.41%; P =.26). In responding patients, median DOR (from randomization to progression) was 19.0 months for fulvestrant and 10.8 months for anastrozole. Using all patients, DOR was significantly greater for fulvestrant compared with anastrozole; the ratio of average response durations was 1.35 (95% CI, 1.10 to 1.67; P < 0.01). Both treatments were well tolerated.

CONCLUSION

Fulvestrant was at least as effective as anastrozole, with efficacy end points slightly favoring fulvestrant. Fulvestrant represents an additional treatment option for postmenopausal women with advanced breast cancer whose disease progresses on tamoxifen therapy.

Fulvestrant

Fulvestrant, a novel oestrogen receptor (ER) downregulator, is a pure anti-oestrogen which completely blocks the trophic actions of oestrogens without exerting any partial agonist effects. It reduces expression of oestrogen receptor, progesterone receptor and proliferative and cell turnover indices. The drug is well-tolerated with minimal systemic side effects. Large randomised trials have demonstrated similar efficacy to anastrozole in the treatment of postmenopausal advanced breast cancer. While results of a Phase III trial comparing fulvestrant with tamoxifen as first-line endocrine therapy for postmenopausal advanced breast cancer are awaited, future studies on its role in adjuvant and neoadjuvant settings, as well as in premenopausal women are required. With the role of tamoxifen as the gold standard of first-line therapy being challenged by the third generation aromatase inhibitors, direct comparison of the latter with fulvestrant in the first-line setting may also be worthwhile.

Faslodex (ICI 182, 780), a novel estrogen receptor downregulator--future possibilities in breast cancer

Tamoxifen is an effective treatment for breast cancer; however, as well as exerting antagonistic effects on the estrogen receptor (ER), tamoxifen acts as a partial agonists in estrogen-sensitive tissues, resulting in stimulation of the endometrium and tumor growth in some patients who become resistant to treatment.ICI 182, 780 (Faslodex), a steroidal estrogen antagonist, is the first in a new class of agent-an estrogen receptor downregulator. Pre-clinical breast cancer models show that ICI 182, 780 leads to a prolonged duration of response, and that it exerts its effects via a different mode of action to tamoxifen. This was confirmed in a small clinical study involving 19 post-menopausal advanced breast cancer patients, where ICI 182, 780 was highly effective after tamoxifen failure. Definitive evidence of the differing modes of action of ICI 182, 780 and tamoxifen, were provided in a study involving post-menopausal women with primary breast cancer, where analyses of tumor samples following short-term exposure to both drugs, showed that ICI 182, 780 reduced tumor ER levels in a dose-dependent manner, and to a significantly greater extent than tamoxifen. Additionally, unlike tamoxifen, ICI 182, 780 did not promote ER-mediated progesterone receptor expression, indicating that it lacks estrogen agonist activity. Ongoing studies in post-menopausal women with advanced breast cancer are comparing ICI 182, 780 to anastrozole and tamoxifen, respectively. Future studies being considered are whether ICI 182, 780 may also be effective in breast cancer in pre-menopausal women, in early breast cancer and in ductal carcinoma in situ in the breast, in combination with other hormonals, cytotoxics and biological modifiers.

Fulvestrant

Fulvestrant is a 7alpha-alkylsulphinyl analogue of estradiol that competes with endogenous estrogen for binding to the estrogen receptor. Once bound to the receptor, fulvestrant attenuates receptor dimerisation, effecting a rapid degradation of the estrogen receptor protein and inhibition of transcription. Fulvestrant is a potent inhibitor of the growth of human breast cancer cells in vitro and in vivo. It has demonstrated pure anti-estrogenic activity in animal systems. Intramuscular fulvestrant 250 mg once a month was as effective as the oral aromatase inhibitor anastrozole 1 mg/day in 2 phase III trials in postmenopausal women with advanced breast cancer who had received prior endocrine therapy. Median time to disease progression (the primary end-point) with fulvestrant and anastrozole was 5.4 and 3.4 months (North American trial) and 5.5 and 5.1 months (European trial). The median duration of response was 19.3 and 10.5 months (North American trial) and 14.3 and 14.0 months (European trial). The most common adverse events with fulvestrant are gastrointestinal disturbances and hot flushes. Fulvestrant showed similar tolerability to anastrozole in 2 phase III trials.

Change in expression of ER, bcl-2 and MIB1 on primary tamoxifen and relation to response in ER positive breast cancer

Pre-treatment oestrogen receptor (ER) expression in breast cancer predicts for rate of response to endocrine therapy but not for the quality or duration of response (DofR). ER is known to be down-regulated by anti-oestrogens. This study has tested the hypothesis that the degree of down-regulation of ER and the ER-regulated marker bcl-2 are associated with the quality and duration of tamoxifen response. 80 patients with ER+ve breast cancer (H-score > 10) receiving primary tamoxifen (n = 51 Stage I-II elderly; n = 29 Stage III) underwent sequential tumour biopsies for immunocytochemical assessment of ER, bcl-2 and the proliferation marker MIB1. Median follow-up is 45 months. By 6-months on therapy three patients had attained complete response (CR), 27 partial response (PR); 44 static disease (SD) and six progression (PD) by UICC criteria. Greater decrease in ER and bcl-2 H-score from pre-treatment to 6 weeks (p = 0.035, p = 0.037) and ER and bcl-2 H-score from pre-treatment to 6 months (p = 0.058, p = 0.036) were significantly associated with better quality of response (CR/PR vs SD/PD). Greater 6-week and 6-month reduction in bcl-2 H-score (p = 0.041, p = 0.036) and 6-week reduction in MIB1 (p = 0.013) were significantly correlated with longer DofR. This study demonstrates that greater down-regulation of ER and the ER-regulated protein bcl-2 on primary tamoxifen are significantly associated with a better quality of response and bcl-2 and the proliferation marker MIB1 a longer duration of response in ER+ve breast cancer.

Selective estrogen receptor modulators: structure, function, and clinical use

The sex hormone estrogen is important for many physiologic processes. Prolonged stimulation of breast ductal epithelium by estrogen, however, can contribute to the development and progression of breast cancer, and treatments designed to block estrogen's effects are important options in the clinic. Tamoxifen and other similar drugs are effective in breast cancer prevention and treatment by inhibiting the proliferative effects of estrogen that are mediated through the estrogen receptor (ER). However, these drugs also have many estrogenic effects depending on the tissue and gene, and they are more appropriately called selective estrogen receptor modulators (SERMs). SERMs bind ER, alter receptor conformation, and facilitate binding of coregulatory proteins that activate or repress transcriptional activation of estrogen target genes. Theoretically, SERMs could be synthesized that would exhibit nearly complete agonist activity on the one hand or pure antiestrogenic activity on the other. Depending on their functional activities, SERMs could then be developed for a variety of clinical uses, including prevention and treatment of osteoporosis, treatment and prevention of estrogen-regulated malignancies, and even for hormone replacement therapy. Tamoxifen is effective in patients with ER-positive metastatic breast cancer and in the adjuvant setting. The promising role for tamoxifen in ductal carcinoma-in-situ or for breast cancer prevention is evolving, and its use can be considered in certain patient groups. Other SERMs are in development, with the goal of reducing toxicity and/or improving efficacy, and future agents have the potential of providing a new paradigm for maintaining the health of women.

ICI 182,780 (Faslodex): development of a novel, "pure" antiestrogen

BACKGROUND

The nonsteroidal antiestrogen tamoxifen is well established as an effective treatment for patients with breast carcinoma, both for the treatment of metastatic disease and as an adjuvant to surgery for patients with primary breast carcinoma. In addition to exerting antagonistic effects on the estrogen receptor, tamoxifen and its derivatives act as partial agonists on certain tissues. These agonistic effects, for example, endometrial stimulation and stimulation of tumor growth after previous response to tamoxifen, may limit their clinical efficacy. ICI 182,780 (Faslodex) from AstraZeneca (Cheshire, United Kingdom) is a novel, steroidal estrogen antagonist that was designed to be devoid of estrogen agonist activity in preclinical models.

METHODS

ICI 182,780 was tested in a large number of in vitro and in vivo preclinical models, and its value was assessed clinically when administered before surgery for breast carcinoma and hysterectomy for benign conditions and after failure of tamoxifen in patients with advanced breast carcinoma.

RESULTS

All data indicated that ICI 182,780 is devoid of agonist activity in preclinical models and in clinical trials. It inhibits growth of the breast and endometrium. In animal models, it does not cross the blood-brain barrier and appears to be neutral with respect to lipids and bone. ICI 182,780 down-regulates the estrogen receptor and is active in tamoxifen-resistant breast carcinoma. In a small, Phase II study, durable responses were seen: Phase III clinical trials are in progress comparing ICI 182,780 with anastrozole and tamoxifen in the treatment of patients with advanced breast carcinoma.

CONCLUSIONS

ICI 182,780 specifically down-regulates the estrogen receptor and, thus, represents the first of a new class of therapeutic agents. In this report, the authors present the current evidence that distinguishes ICI 182,780 from tamoxifen and related nonsteroidal compounds and establishes ICI 182,780 as the first in a new class of therapeutic agents.

Is there a growing role for endocrine therapy in the treatment of breast cancer?

Novel biochemical findings on the molecular mechanisms of estrogen actions may help us to understand some of the unexplained observations seen in breast cancer treatment and suggest new therapeutic opportunities. Thus, apart from the challenge of improving the clinical treatment of patients with advanced disease, results from trials in this setting may reveal new therapeutic principles that may be evaluated in the adjuvant setting. The role of endocrine therapy in metastatic as well as early breast cancer is increasing, and the possibility of improving cure rates for breast cancer by implementing therapy with novel aromatase inhibitors in the adjuvant setting is exciting. While the results from prevention trials are most interesting, suggesting the possibility of reducing breast cancer incidence in high-risk groups, more data are needed before we can decide whether such interventions are warranted in women at high risk of developing breast cancer.

Selective oestrogen receptor modifiers (SERMs) and breast cancer therapy

Antioestrogen therapy is currently receiving renewed interest for several reasons. Tamoxifen was introduced in the treatment of metastatic breast cancer more than three decades ago. The drug significantly reduces long term mortality and also reduces the risk of contralateral tumours when administered in early breast cancer. Five years of tamoxifen is now standard in adjuvant endocrine therapy, and the drug is currently being evaluated for breast cancer prevention. Despite this, several aspects regarding the pharmacology of the drug are still unclear, and the scientific rationale for dose selection has recently been challenged. Several novel antioestrogen compounds, called selective oestrogen receptor modifiers (SERMs), express selective oestrogen agonistic or antagonistic properties depending on the organ or test system evaluated. Some of these drugs, like raloxifene, do not seem to promote the development of endometrial cancer, although they still have selected oestrogen-like beneficial effects. This paper reviews the pharmacologic and the pharmacokinetic aspects of the different SERMs with particular emphasis on their potential use in therapy and prevention of breast cancer.

Modern antioestrogens and the coming revolution in women's health care

This review will focus on antioestrogens and selective oestrogen receptor modulators (SERMS). The more traditional SERMS, clomiphene citrate and tamoxifen, will be reviewed along with such modern drugs as raloxifene and faslodex, with emphasis upon their actions on breast, uterus, bone and lipids. The future potential of these medications, in the management of oestrogen-dependent gynaecological conditions such as endometriosis, dysfunctional uterine bleeding, fibroids and breast cancer will be discussed.