Effects of fulvestrant 250mg in premenopausal women with oestrogen receptor-positive primary breast cancer

Oral Selective Estrogen Receptor Degraders (SERDs) in Breast Cancer: Advances, Challenges, and Current Status

Several endocrine therapies are currently available for the treatment of estrogen receptor (ER) positive breast cancer, but the clinical benefit of these agents is limited by endocrine therapy drug resistance. A common mechanism of endocrine therapy resistance is ESR1 mutations. The first-generation selective estrogen receptor degrader (SERD) fulvestrant has activity against ESR1 mutant tumors but requires intramuscular injection and has poor bioavailability that precludes optimal drug dosing. This led to the development of second-generation SERDs which are potent and have improved oral bioavailability and pharmacokinetics. Several of these oral SERDs are now in phase III trials in both the early and advanced ER positive breast cancer settings. This review summarizes the background of oral SERD development, the current status and future perspectives.

The Role of Gonadotropin-Releasing-Hormone Analogues in the Treatment of Breast Cancer

The prognosis of premenopausal breast cancer patients with early disease has improved over the past decades, particularly in women expressing hormone receptors in their tumors. Tamoxifen, a selective estrogen receptor modulator, has dramatically changed outcomes in these patients and remains one of the standards of care. Ovarian function suppression by gonadotropin-releasing-hormone analogues (GnRHa) represents an additional treatment option. Long-term data are required before firm conclusions can be drawn, whereas recent clinical trials suggest that the use of GnRHa is effective in both adjuvant and metastatic settings, particularly in younger patients (<35 years old). The decision to select the optimal therapy should be individualized according to the biological characteristics of tumors, estimates of disease response, comorbidities, patient preference, and long-term toxicity.

Novel flexible heteroarotinoid, SL-1-18, promotes ERα degradation to inhibit breast cancer cell growth

SL-1-18 (1-(chrysen-6-yl)-3-(4-nitrophenyl)thiourea) is new flexible heteroarotinoid (Flex-Het) analog derived from the parent compound, SHetA2, and our previous study showed comparable activity to SHetA2 in terms of inhibiting ER+ breast cancer cell growth. This current study aims to determine the molecular mechanism underlying SL-1-18's effect on breast cancer cell growth. Our results indicate that SL-1-18 inhibits cell proliferation of ER+ breast cancer cells (MCF-7 and T-47D) by preventing cell cycle progression. SL-1-18 treatment correlated positively with decreased expression of key cell-cycle regulators, such as cyclin D1, as well as other ERα-target genes at both the transcript and protein levels. Interestingly, decreased expression of ERα was also observed, with a significant reduction at the protein level within 2 h of SL-1-18 treatment, while the decrease in mRNA occurred at a later time point. ERα degradation was shown to be mediated by the ubiquitination-proteasome pathway. In summary, this is the first study to show that a Flex-Het- SL-1-18- can promote the degradation of ERα via the ubiquitin-proteasome pathway and should be further developed as a therapeutic option for ER+ breast cancer.

Palbociclib Combined with Fulvestrant in Premenopausal Women with Advanced Breast Cancer and Prior Progression on Endocrine Therapy: PALOMA-3 Results

BACKGROUND

The efficacy and safety of palbociclib, a cyclin-dependent kinase 4/6 inhibitor, combined with fulvestrant and goserelin was assessed in premenopausal women with advanced breast cancer (ABC) who had progressed on prior endocrine therapy (ET).

PATIENTS AND METHODS

One hundred eight premenopausal endocrine-refractory women ≥18 years with hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) ABC were among 521 women randomized 2:1 (347:174) to fulvestrant (500 mg) ± goserelin with either palbociclib (125 mg/day orally, 3 weeks on, 1 week off) or placebo. This analysis assessed whether the overall tolerable safety profile and significant progression-free survival (PFS) improvement extended to premenopausal women. Potential drug-drug interactions (DDIs) and ovarian suppression with goserelin were assessed via plasma pharmacokinetics and biochemical analyses, respectively. (ClinicalTrials.gov identifier: NCT01942135) RESULTS: Median PFS for premenopausal women in the palbociclib (n = 72) versus placebo arm (n = 36) was 9.5 versus 5.6 months, respectively (hazard ratio, 0.50, 95% confidence interval: 0.29-0.87), and consistent with the significant PFS improvement in the same arms for postmenopausal women. Any-grade and grade ≤3 neutropenia, leukopenia, and infections were among the most frequent adverse events reported in the palbociclib arm with concurrent goserelin administration. Hormone concentrations were similar between treatment arms and confirmed sustained ovarian suppression. Clinically relevant DDIs were not observed.

CONCLUSION

Palbociclib combined with fulvestrant and goserelin was an effective and well-tolerated treatment for premenopausal women with prior endocrine-resistant HR+/HER2- ABC. Inclusion of both premenopausal and postmenopausal women in pivotal combination ET trials facilitates access to novel drugs for young women and should be considered as a new standard for clinical trial design.

IMPLICATIONS FOR PRACTICE

PALOMA-3, the first registrational study to include premenopausal women in a trial investigating a CDK4/6 inhibitor combined with endocrine therapy, has the largest premenopausal cohort reported in an endocrine-resistant setting. In pretreated premenopausal women with hormone receptor-positive advanced breast cancer, palbociclib plus fulvestrant and goserelin (luteinizing hormone-releasing hormone [LHRH] agonist) treatment almost doubled median progression-free survival (PFS) and significantly increased the objective response rate versus endocrine monotherapy, achieving results comparable to those reported for chemotherapy without apparently interfering with LHRH agonist-induced ovarian suppression. The significant PFS gain and tolerable safety profile strongly support use of this regimen in premenopausal women with endocrine-resistant disease who could possibly delay chemotherapy.

Endocrine therapy in post-menopausal women with metastatic breast cancer: From literature and guidelines to clinical practice

Current international guidelines recommend endocrine therapy as the initial treatment of choice in hormone receptor positive advanced breast cancer. Endocrine therapy has been a mainstay of hormone responsive breast cancer treatment for more than a century. To date it is based on different approaches,such as blocking the estrogen receptor through selective receptor estrogen modulators, depleting extragonadal peripheral estrogen synthesis by aromatase inhibitors or inducing estrogen receptor degradation using selective down-regulators. Despite estrogen and/or progesterone receptor positive status, up to a quarter of patients could be either primarily resistant to hormone therapies or will develop hormone resistance during the course of their disease. Different mechanisms, either intrinsic or acquired, could be implicated in endocrine resistance. In the present work available endocrine therapies and their appropriate sequences have been reviewed, and the most promising strategies to overcome endocrine resistance have been highlighted.

Biological effects of fulvestrant on estrogen receptor positive human breast cancer: short, medium and long-term effects based on sequential biopsies

We report the first study of the biological effect of fulvestrant on ER positive clinical breast cancer using sequential biopsies through to progression. Thirty-two locally/systemically advanced breast cancers treated with first-line fulvestrant (250 mg/month) were biopsied at therapy initiation, 6 weeks, 6 months and progression and immunohistochemically-analyzed for Ki67, ER, EGFR and HER2 expression/signaling activity. This series showed good fulvestrant responses (duration of response [DoR] = 25.8 months; clinical benefit = 81%). Ki67 fell (p < 0.001) in 79% of tumours by 6 months and lower Ki67 at all preprogression time-points predicted for longer DoR. ER and PR significantly decreased in all tumours by 6 months (p < 0.001), with some declines in ER (serine 118) phosphorylation and Bcl-2 (p = 0.007). There were modest HER2 increases (p = 0.034, 29% tumours) and loss of any detectable EGFR phosphorylation (p = 0.024, 50% tumours) and MAP kinase (ERK1/2) phosphorylation (p = 0.019, 65% tumours) by 6 months. While ER remained low, there was some recovery of Ki67, Bcl-2 and (weakly) EGFR/MAPK activity in 45-67% patients at progression. Fulvestrant's anti-proliferative impact is related to DoR, but while commonly downregulating ER and indicators of its signaling and depleting EGFR/MAPK signaling in some patients, additional elements must determine response duration. Residual ER at fulvestrant relapse explains reported sensitivity to further endocrine therapies. Occasional modest treatment-induced HER2 and weakly detectable EGFR/HER2/MAPK signaling at relapse suggests targeting of such activity might have value alongside fulvestrant in some patients. However, unknown pathways must drive relapse in most. Ki67 has biomarker potential to predict fulvestrant outcome and as a quantitative measure of response.

New insights into endocrine therapy for young women with breast cancer

Managing estrogen receptor-positive breast cancer in young women (<40 years) requires a multidisciplinary/personalized approach, covering both clinical and psychosocial aspects. Five years of tamoxifen has been the standard adjuvant endocrine therapy for many years. Recent data from the adjuvant randomized trials TEXT-SOFT show that the aromatase inhibitor exemestane plus ovarian suppression significantly reduces recurrences as compared with tamoxifen plus ovarian suppression. The ATLAS and aTToM trials represent the first evidence of a beneficial effect of extended endocrine therapy with tamoxifen in premenopausal women. Outside of a clinical trial, no data support neoadjuvant endocrine therapy in young women. In the metastatic setting, tamoxifen or aromatase inhibitors, both with ovarian suppression/ablation, should be the preferred choice, unless rapid tumor shrinkage is needed. No data are available with fulvestrant in young patients.

A good drug made better: the fulvestrant dose-response story

Sequential use of endocrine therapies remains the cornerstone of treatment for hormone receptor-positive advanced breast cancer, before the use of cytotoxic chemotherapy for unresponsive disease. Fulvestrant is an estrogen receptor (ER) antagonist approved for the treatment of postmenopausal women with ER+ advanced breast cancer after failure of prior antiestrogen therapy. Initially approved at a monthly dose of 250 mg, the recommended fulvestrant dose was revised to 500 mg (500 mg/mo plus 500 mg on day 14 of month 1) after demonstration of improved progression-free survival versus fulvestrant 250 mg. We have reviewed the dose-dependent effects of fulvestrant, both from a retrospective combined analysis of dose-dependent reduction of tumor biomarkers in the presurgical setting (3 previously reported studies: Study 18, Neoadjuvant Endocrine Therapy for Women with Estrogen-Sensitive Tumors, and Trial 57) and from a review of clinical studies for advanced breast cancer in postmenopausal women. Analysis of presurgical data revealed a consistent dose-dependent effect for fulvestrant on tumor biomarkers, with increasing fulvestrant dose resulting in greater reductions in ER, progesterone receptor, and Ki67 labeling index. The dose-dependent biological effect corresponds with the dose-dependent clinical efficacy observed in the treatment of advanced breast cancer after failure of prior antiestrogen therapy. Although it remains to be determined in a phase III trial, cross-trial comparisons suggest a dose-dependent relationship for fulvestrant as first-line treatment for advanced breast cancer. Overall, biological and clinical data demonstrate a strong dose-dependent relationship for fulvestrant, supporting the efficacy benefit seen with fulvestrant 500 mg over the 250 mg dose.

First international consensus guidelines for breast cancer in young women (BCY1)

The 1st International Consensus Conference for Breast Cancer in Young Women (BCY1) took place in November 2012, in Dublin, Ireland organized by the European School of Oncology (ESO). Consensus recommendations for management of breast cancer in young women were developed and areas of research priorities were identified. This manuscript summarizes these international consensus recommendations, which are also endorsed by the European Society of Breast Specialists (EUSOMA).

Hormonal therapies in young breast cancer patients: when, what and for how long?

Breast cancer in young women (<40 years) is a rare and complex clinical and psychosocial condition, which deserves multidisciplinary and personalized approaches. In young women with hormone-receptor positive disease, 5 years of adjuvant tamoxifen, with or without ovarian suppression/ablation, is considered the standard endocrine therapy. The definitive role of adjuvant aromatase inhibitors has still to be elucidated: the upcoming results of the Tamoxifen and EXemestane Trial (TEXT) and Suppression of Ovarian Function Trial (SOFT) trials will help understanding if we can widen our current endocrine therapeutic options. The optimal duration of adjuvant endocrine therapy in young women also remains an unresolved issue. The recently reported results of the ATLAS and aTToM trials represent the first evidence of a beneficial effect of extended endocrine therapy in premenopausal women and provide an important opportunity in high-risk young patients. In the metastatic setting, endocrine therapy should be the preferred choice for endocrine responsive disease, unless there is evidence of endocrine resistance or need for rapid disease and/or symptom control. Tamoxifen in combination with ovarian suppression/ablation remains the 1st-line endocrine therapy of choice. Aromatase inhibitors in combination with ovarian suppression/ablation can be considered after progression on tamoxifen and ovarian suppression/ablation. Fulvestrant has not yet been studied in pre-menopausal women. Specific age-related treatment side effects (i.e., menopausal symptoms, change in body image and weight gain, cognitive function impairment, fertility damage/preservation, long-term organ dysfunction, sexuality) and the social impact of diagnosis and treatment (i.e., job discrimination, family management) should be carefully addressed when planning long-lasting endocrine therapies in young women with hormone-receptor positive early and advanced breast cancer.

Hormone-related pharmacokinetic variations associated with anti-breast cancer drugs

INTRODUCTION

Breast cancer is the most common female cancer, with more than one million new patients diagnosed annually worldwide. Generally speaking, there are three types of drugs used in management of breast cancer namely: hormonal treatment, chemotherapeutic agents and target-based agents. There is increasing evidence that hormones play an important role in development of both hormone-dependent and hormone-independent breast cancers.

AREAS COVERED

This review summarizes the pharmacokinetics of various types of drugs used to treat breast cancer. Furthermore, the authors discuss hormone-related variations including: the menstrual status, gender and exogenous hormones influencing drug absorption, distribution, metabolism or excretion (ADME). The authors also describe the physiological factors such as body weight and age that affect the pharmacokinetics of several drugs.

EXPERT OPINION

The factors affecting the pharmacokinetics of anti-breast cancer drugs are multifaceted. Hormones appear to be a key factor determining the pharmacokinetics (and efficacy) of hormonal therapy due to their role in cancer progression. In chemotherapy, the effects of hormones on the drug pharmacokinetics are possibly mediated through P-glycoprotein (P-gp) efflux and/or cytochrome P450 metabolism. In many cases, dosing regimen should be adjusted for drugs used in treatment of breast cancers based on the hormone levels in the body.

Current status and future perspectives in the endocrine treatment of postmenopausal, hormone receptor-positive metastatic breast cancer

INTRODUCTION

Endocrine therapy is a fundamental component of the therapeutic repertoire for treatment of metastatic, hormone receptor-positive breast cancer. Inevitably, however, tumors develop resistance to these compounds, and overcoming this phenomenon is a key motivator of research in this field.

AREAS COVERED

This review summarizes the current status of endocrine therapy for the treatment of metastatic disease, with a main focus on postmenopausal patients. Furthermore, strategies that could potentially sustain endocrine resistance and future perspectives in this direction are also to be described. Relevant references were identified by PubMed searches and from the abstract books of the annual meetings of The European Society of Clinical Oncology (ESMO), The American Society of Clinical Oncology (ASCO) and from the San Antonio Breast Cancer Symposia.

EXPERT OPINION

Combinations of endocrine therapy with HER2 targeting agents, as well as with compounds that can interfere with PI3K/Akt/mTOR signaling, are two promising strategies for delaying or overcoming endocrine resistance, mediated by these relevant biological pathways. Due to increased costs and the burden of toxicity associated with these combination therapies, compared to endocrine therapy alone, it is imperative to concentrate efforts on establishing biomarkers that can predict efficacy.

Identification of RNA targets for the nuclear multidomain cyclophilin atCyp59 and their effect on PPIase activity

AtCyp59 is a multidomain cyclophilin containing a peptidyl-prolyl cis/trans isomerase (PPIase) domain and an evolutionarily highly conserved RRM domain. Deregulation of this class of cyclophilins has been shown to affect transcription and to influence phosphorylation of the C-terminal repeat domain of the largest subunit of the RNA polymerase II. We used a genomic SELEX method for identifying RNA targets of AtCyp59. Analysis of the selected RNAs revealed an RNA-binding motif (G[U/C]N[G/A]CC[A/G]) and we show that it is evolutionarily conserved. Binding to this motif was verified by gel shift assays in vitro and by RNA immunopreciptation assays of AtCyp59 in vivo. Most importantly, we show that binding also occurs on unprocessed transcripts in vivo and that binding of specific RNAs inhibits the PPIase activity of AtCyp59 in vitro. Surprisingly, genome-wide analysis showed that the RNA motif is present in about 70% of the annotated transcripts preferentially in exons. Taken together, the available data suggest that these cyclophilins might have an important function in transcription regulation.

The European Society of Breast Cancer Specialists recommendations for the management of young women with breast cancer

EUSOMA (The European Society of Breast Cancer Specialists) is committed to writing recommendations on different topics of breast cancer care which can be easily adopted and used by health professionals dedicated to the care of patients with breast cancer in their daily practice. In 2011, EUSOMA identified the management of young women with breast cancer as one of the hot topics for which a consensus among European experts was needed. Therefore, the society recently organised a workshop to define such recommendations. Thirteen experts from the different disciplines met for two days to discuss the topic. This international and multidisciplinary panel thoroughly reviewed the literature in order to prepare evidence-based recommendations. During the meeting, two working groups were set up to discuss in detail diagnosis and loco-regional and systemic treatments, including both group aspects of psychology and sexuality. The conclusions reached by the working groups were then discussed in a plenary session to reach panel consensus. Whenever possible, a measure of the level of evidence (LoE) from 1 (the highest) to 4 (the lowest) degree, based on the methodology proposed by the US Agency for Healthcare Research and Quality (AHRQ), was assigned to each recommendation. The present manuscript presents the recommendations of this consensus group for the management of young women with breast cancer in daily clinical practice.

Ovarian function suppression and fulvestrant as endocrine therapy in premenopausal women with metastatic breast cancer

BACKGROUND

Endocrine therapy is the preferred treatment for hormone-receptor (HR) positive metastatic breast cancer. In premenopausal patients, ovarian function suppression with goserelin in combination with anastrozole yielded promising results in phase II studies. Fulvestrant, a pure antioestrogen, yields high rates of disease stabilisation in postmenopausal women. Therefore, we investigated the feasibility and safety of fulvestrant plus goserelin in premenopausal women with HR-positive metastatic breast cancer.

METHODS

Premenopausal patients with metastatic breast cancer eligible for endocrine treatment received fulvestrant 250 mg and goserelin 3.6 mg every four weeks as first- to fourth-line therapy. Clinical benefit rate (CBR; response rate plus disease stabilisation ≥ 6 months) was defined as the primary study end-point. Time to progression (TTP) and overall survival (OS) were estimated using the Kaplan-Meier product limit method.

FINDINGS

Twenty-six patients received treatment as scheduled. 81% were pre-treated with tamoxifen and 69% had received prior aromatase inhibitors in combination with goserelin. The majority of patients (69%) presented with visceral metastases. Complete response was observed in a single patient, partial response in three and disease stabilisation ≥ 6 months in eleven patients, resulting in a CBR of 58%. Median TTP was 6 months (95%confidence interval (CI), 2.4-9.6) and OS 32 months (95%CI, 14.28-49.72), respectively.

INTERPRETATION

Results suggest that the combination of fulvestrant and goserelin offers promising activity in premenopausal patients and further investigation is warranted.

Synergistic effects of parabens on the induction of calbindin-D9k gene expression act via a progesterone receptor-mediated pathway in GH3 cells

Although the endocrine-disrupting bioactivity of parabens is weakly estrogenic (parabens are xenoestrogens), their combined synergistic effect is unknown. The aim of this study was to investigate the effects of methyl paraben (MP), ethyl paraben (EP), propyl paraben (PP), isopropyl paraben (IPP), butyl paraben (BP), and isobutyl paraben (IBP), either alone or in combination (MP + EP + PP + BP; PP + IPP; and BP + IBP) on the induction of the estrogenic biomarker gene, calbindin-D9k( CaBP-9k), in rat pituitary lactosomatotrophic GH3 cells. The expression of CaBP-9k mRNA and protein was analyzed using real-time PCR and Western blot analysis, respectively. After 24 h of treatment, a significant increase in CaBP-9k expression was observed. This was dependent upon the length of the paraben alkyl chains (shortest in MP and longest in IBP). Interestingly, the synergistic effects of these paraben combinations were observed at a dose (10−5 M) of these parabens, which induced the highest expression of CaBP-9k mRNA and protein. To investigate the involvement of estrogen receptors (ERs) and progesterone receptors (PRs), through which parabens exert their effects, the expression levels of ERα and PR-B were also examined. The expression of ERα mRNA and protein fluctuated after paraben treatment in GH3 cells, which was not significant. However, the expression level of ERα gene was induced when cotreated with 17β-estradiol (E2) and ICI 182, 780 (estrogen receptor antagonist). The different combinations of parabens induced the expression of the PR-B gene, which was abolished by cotreatment with ICI 182,780. The expression patterns of CaBP-9k and PR-B genes appeared to be similar in response to paraben treatments. This implied that CaBP-9k expression in GH3 cells may be induced by parabens via a PR-mediated pathway. Taken together, these results suggest that exposure to multiple parabens at low concentrations may increase their synergistic estrogenic activities in GH3 cells through a PR-mediated pathway.

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.

Management of patients with metastatic breast cancer

Hormone treatment is one of the key strategies in the management of metastatic breast cancer. Hormone treatment is one of the key strategies in the management of metastatic breast cancer. Aromatase inhibitors (AI) have been extensively studied in this setting. This section summarizes the key data regarding the use of AI in advanced breast cancer. In postmenopausal women, AI are the first line of treatment for untreated patients, or those who had prior AI treatment and progress after 12 months of adjuvant therapy. A longer disease-free interval and absence of visceral disease is associated with a better response. If tumors recur in less than 12 months, it is recommended that tamoxifen (TAM) or the estrogen-receptor antagonist fulvestrant (FUL) treatment be initiated. In the second-line setting, the best option after progression is the administration of either FUL or TAM. In the third-line setting, reintroduction of AI is considered an acceptable option. In premenopausal women who have not received prior treatment or who have progressed after 12 months following adjuvant treatment, it is recommended to initiate therapy with a combination of TAM and a luteinizing hormone-releasing hormone (LHRH) analog. If there is treatment failure with the use of this combination, megestrol acetate or an LHRH agonist plus an AI may be reasonable alternatives. Intensive research is ongoing to understand the mechanisms of resistance to hormone therapy. In human epidermal growth factor receptor 2 positive-patients, combinations with HER2 antagonists are associated with significant clinical activity.

Fulvestrant: a unique antiendocrine agent for estrogen-sensitive breast cancer

IMPORTANCE OF THE FIELD

The role of estrogen deprivation for the treatment of breast cancer has been understood since the 1800s. Pharmacologic advances in the field in the past decades, including tamoxifen and the aromatase inhibitors, have contributed significantly to the reduced mortality of estrogen-sensitive breast cancer. However, this subtype of breast cancer still presents with relapses and, once metastatic, progression to hormone-refractory state and loss of disease control remain an expected disease course. Fulvestrant, a pure estrogen receptor downregulator, is a new addition to the antiestrogen therapeutic armamentarium since its FDA approval in 2002. Its unique mechanism of action offers potential advantages over other estrogen targeted therapies.

AREAS COVERED IN THIS REVIEW

Published scientific literature, including presented abstracts, on fulvestrant from 1985 to the present were reviewed with selected publications included.

WHAT THE READER WILL GAIN

This review addresses current issues and therapies for estrogen-sensitive breast cancer, highlights the role of fulvestrant in current treatment guidelines and outlines some of the ongoing investigations of this compound.

TAKE HOME MESSAGE

Fulvestrant is an effective and well-tolerated drug for treatment of metastatic estrogen-sensitive breast cancer. Work is underway to enhance its clinical benefit to patients as a single agent and in combination with other therapies.

Endocrine therapy of metastatic breast cancer

Breast cancer growth and dissemination is regulated by estrogen and different growth factor receptor signalling pathways. The increasing knowledge of the biology of breast cancer regarding the interaction of these signalling pathways provides a tool to understand endocrine therapies response and resistance mechanisms. In patients with slowly progressive disease, no visceral involvement, and minimal symptoms, endocrine therapy could be the strategy of choice, even if the tumor has low estrogen receptor expression. Ovarian suppression and tamoxifen are recommended for premenopausal patients whether aromatase inhibitors are the option for postmenopausal ones. Chemotherapy still remains as the right alternative for hormone unresponsive or resistant patients. This is a review focused on the different strategies and combinations of endocrine therapies for metastatic breast cancer patients considering the potential strategies clinically tested to overcome resistance and the different treatments of choice available for each scenario of disseminated disease.

Fulvestrant (Faslodex) -- how to make a good drug better

Fulvestrant (Faslodex); AstraZeneca Pharmaceuticals, Wilmington, DE) is an estrogen receptor (ER) antagonist with a novel mode of action; it binds, blocks, and increases degradation of ER. Fulvestrant (at the approved dose [250 mg/month]) is at least as effective as anastrozole (1 mg/day) in the treatment of postmenopausal women with hormone receptor-positive advanced breast cancer (HR(+) ABC) progressing or recurring on antiestrogen therapy, and is also an active first-line treatment. Although fulvestrant (250 mg/month) is clearly effective, it takes 3-6 months to achieve steady-state plasma levels. Steady-state concentrations are approximately twofold higher than those achieved with a single dose; reaching this earlier, for example, via a loading-dose (LD) regimen (250 mg/month plus 500 mg on day 0 and 250 mg on day 14 of month 1), may allow responses to be achieved more quickly and limit the possibility of early relapse. Fulvestrant high-dose (HD) regimens (500 mg/month) offer the possibility of greater antitumor activity, because (a) ER downregulation is a dose-dependent process (an approximately 70% reduction is observed with a single 250 mg dose of fulvestrant) and (b) evidence correlates greater ER downregulation with superior efficacy. A fulvestrant HD regimen offers the potential of achieving near 100% ER downregulation. There is also potential to increase fulvestrant-ER binding by reducing plasma estrogen levels, for example, with concomitant aromatase inhibitor treatment. Several ongoing trials use LD, HD, and combination regimens; results from these studies are awaited with interest. Meanwhile, fulvestrant (250 mg/month) remains a valuable additional endocrine treatment for postmenopausal women with HR(+) ABC recurring or progressing on antiestrogen therapy.

Definition of functionally important mechanistic differences among selective estrogen receptor down-regulators

One subclass of antiestrogens, the selective estrogen receptor down-regulators (SERDs), have received considerable attention of late as they competitively inhibit estrogen binding and induce a rapid, proteasome-dependent degradation of the receptor. Contained within this class of molecules is the steroidal antiestrogen ICI182,780 (faslodex), recently approved for the treatment of metastatic cancer, and GW5638/DPC974, a SERD that is currently being evaluated in the clinic. Given that mechanistic differences between different selective estrogen receptor modulators have been translated into important clinical profiles, it was of interest to determine if the SERD subclass of ligands were likewise functionally or mechanistically distinguishable. In this study, we show that although the steroidal and nonsteroidal SERDs target ERalpha for degradation, the underlying mechanism(s) are different. Of note was the identification of a specific protein-protein interaction surface presented on ERalpha in the presence of the ICI182,780-activated receptor which is required for degradation. Interestingly, this surface is also presented on ERalpha in the presence of RU58,668, a SERD that is chemically distinct from ICI182,780. This surface is not required for GW5638-mediated degradation, and thus, this SERD seems to affect ERalpha down-regulation by a different mechanism. These data suggest that sequencing of therapies using drugs of this class is likely to be possible. Finally, because of the unmet need for orally active SERDS that function similarly to ICI182,780, we have used the insights from these mechanistic studies to develop and validate a high-throughput screen for compounds of this class with improved pharmaceutical properties.

Controversies of adjuvant endocrine treatment for breast cancer and recommendations of the 2007 St Gallen conference

Endocrine treatment for breast cancer was introduced more than a century ago. The discovery of hormone receptors has allowed targeting of endocrine treatment to patients whose primary tumours express these receptors. In the adjuvant setting, different approaches are used in premenopausal or postmenopausal women. In premenopausal patients, suppression of ovarian function and the use of tamoxifen are the most important therapeutic options, even though questions on timing, duration, and combination of these compounds remain unanswered. The use of aromatase inhibitors in combination with ovarian-function suppression is currently under investigation in the premenopausal setting. In postmenopausal patients, aromatase inhibitors given after 2-3 years or 5 years of tamoxifen have shown a significant benefit over tamoxifen alone. However, questions on this treatment also remain unanswered. For example, whether all patients should receive an aromatase inhibitor or whether some subgroups of patients might be optimally treated by tamoxifen alone is yet to be established. In this paper we review the published work on adjuvant endocrine treatment in breast cancer and provide recommendations from the 2007 St Gallen International Conference on Primary Therapy of Early Breast Cancer.