Superior efficacy of letrozole versus tamoxifen as first-line therapy for postmenopausal women with advanced breast cancer: results of a phase III study of the International Letrozole Breast Cancer Group

Anti-oestrogenic chemoprevention of breast cancer-the need to progress

Clinical trials of the selective oestrogen receptor modulator (SERM), tamoxifen, have shown an early reduction in risk of breast cancer in healthy women of approximately 40%, but with associated risks and benefits to normal tissues. An overall clinical benefit and the identification of the women at risk of breast cancer who may gain benefit from tamoxifen has not been clearly established. The identification of those women at risk who are most likely to gain benefit, and the development of other SERMs and aromatase inhibitors which might be more active and have a more beneficial spectrum of activity on normal tissues in healthy women is essential, if the aim of preventing breast cancer in healthy women is to be achieved.

Effect of antiestrogens and aromatase inhibitor on basal growth of the human breast cancer cell line MCF-7 in serum-free medium

Antiestrogens are efficient inhibitors of estrogen-mediated growth of human breast cancer. Besides inhibiting estradiol-stimulated growth, antiestrogens may have a direct growth-inhibitory effect on estrogen receptor (ER) positive cells and thus be more efficient than aromatase inhibitors, which will only abrogate estrogen-dependent tumor growth. To address this issue, we have used the human breast cancer cell line MCF-7/S9 as a model system which is maintained in a chemically defined medium without serum and estrogen. The addition of estradiol results in an increase in cell growth rate. Thus, the MCF-7/S9 cell line is estrogen-responsive but not estrogen-dependent. Three different types of antiestrogens, namely tamoxifen, ICI 182,780 and EM-652 were found to exert a significant and dose-dependent inhibition of basal growth of MCF-7/S9 cells. The growth-inhibitory effect of the three antiestrogens was prevented by simultaneous estradiol treatment. Antiestrogen treatment also reduced the basal pS2 mRNA expression level, thus indicating spontaneous estrogenic activity in the cells. However, treatment with the aromatase inhibitor had no effect on basal cell growth, excluding that endogenous estrogen synthesis is involved in basal growth. These data demonstrate that in addition to their estrogen antagonistic effect, antiestrogens have a direct growth-inhibitory effect which is ER-mediated. Consequently, in the subset of ER positive breast cancer patients with estrogen-independent tumor growth, antiestrogen therapy may be superior to treatment with aromatase inhibitors which only inhibit estrogen formation but do not affect cancer cell growth in the absence of estrogens.

Study of suboptimum treatment response: lessons from breast cancer

Drug resistance is the main cause of therapeutic failure and death in patients with cancer. However, there have been surprisingly few studies designed specifically to investigate the mechanisms underlying poor treatment response in vivo, compared with the number of phase II and III trials investigating treatment effects. We can now analyse the expression patterns of multiple genes by use of microarrays, rapid gene sequencing, and proteomics, and so need to reassess the way we design clinical trials to take full advantage of these new opportunities. I discuss the concept of clinical studies of chemoresistance in terms of the collection of tumour samples for biological studies, the use of appropriate clinical settings, and the importance of trial design. Ideally, such studies should investigate specific biological features in relation to measurable antitumour effects of single drugs.

Pathological features of breast cancer response following neoadjuvant treatment with either letrozole or tamoxifen

Morphological characteristics, grading features, proliferation marker MIB1, apoptosis (by Tdt-mediated duTP-biotin nick-end labelling (TUNEL)), Bcl-2 expression, oestrogen receptor (ER) and progesterone receptor (PgR) status were compared in ER-positive breast cancers before and after 3 months of neoadjuvant therapy with either letrozole or tamoxifen. Daily treatment was with letrozole 2.5 mg (12 patients) or 10 mg (12 patients), or with tamoxifen 20 mg(24 patients). Letrozole treatment was associated with a pathological response in 17 of 24 (71%) patients. The predominant change in grading features was a decrease in mitosis, and the expression of MIB1 was reduced in all of the 22 evaluable cases. Whilst only marginal changes were observed in ER expression following letrozole therapy, PgR reactivity was reduced in 20 of 21 evaluable cases which were initially PgR-positive, becoming undetectable in 16 patients. Tamoxifen treatment was associated with pathological response in 15 of 24 (63%) tumours. In contrast to letrozole, the dominant change in grading feature was an increase in tubule formation, ER score was markedly reduced in most cases, and the most common effect on PgR was an increased expression. Following treatment with either tamoxifen or letrozole, variable effects were observed on the apoptotic index and expression of Bcl-2. These results indicate that both letrozole and tamoxifen have marked influences on the pathological features of breast cancer during neoadjuvant therapy. However, the effects of the two agents varied such that the phenotypes of letrozole- and tamoxifen-treated tumours differ markedly. Effects on clinical, pathological and biological endpoints were frequently disconcordant--future studies will therefore require the evaluation of multiple parameters in order to fully assess tumour response.

Adjuvant breast cancer treatment and cognitive function: current knowledge and research directions

Evidence is mounting that potentially curative systemic adjuvant therapy for early-stage breast cancer may result in cognitive impairment. Five published studies have investigated cognitive function in this setting, and the consistent results of all five studies suggest an adverse effect of adjuvant chemotherapy. These studies are reviewed with particular attention to their methodologic limitations. For example, all five studies used cross-sectional designs, none controlled for possible confounding hormonal factors, and three examined patients who had not received a uniform chemotherapy regimen. The potential roles of chemotherapy-induced menopause and of adjuvant hormonal therapy in cognitive impairment are also discussed. Priorities for future research include confirmation of an effect of adjuvant chemotherapy in a study with a longitudinal design, closer examination of the potential contribution of hormonal factors, and similar studies on the effect of adjuvant therapy on cognitive function in other cancer types. If an effect of systemic adjuvant therapy on cognitive function is confirmed, such an effect will have implications for informed consent. It may also result in incorporation of objective measures of cognition in clinical trials of adjuvant therapy and in the investigation of preventive interventions that might minimize the impact of cognitive dysfunction after cancer treatment.

Current and future status of adjuvant therapy for breast cancer

Adjuvant systemic treatments have greatly improved the prognosis of women with early breast cancer. Combination chemotherapy and, for patients with oestrogen receptor-positive (ER+) tumours, endocrine treatment has been found to reduce the frequency of relapse and improve survival. New adjuvant strategies include the introduction of taxanes into adjuvant chemotherapy schedules, the use of aromatase inhibitors in place of, or in addition to, tamoxifen, and the use of adjuvant bisphosphonates. Combination chemotherapy has been found to reduce the annual odds of recurrence and death in pre- and postmenopausal women. The benefits, however, are on average less in older patients. Anthracycline-based regimens are more effective than traditional regimens of cyclophosphamide, methotrexate, and fluorouracil (CMF). The benefits of adjuvant cytotoxic and endocrine treatments are additive. There is considerable debate as to the role of taxanes in adjuvant therapy. Improved outcome has been observed in one large trial, especially in those patients with ER-negative tumours. High-dose chemotherapy has not fulfilled its early promise. Ovarian suppression and/or tamoxifen remain the treatments of choice. The annual odds of relapse and death have been reduced by approximately one-third and one-quarter, respectively. Several very large studies are in progress to assess the potential of aromatase inhibitors in the adjuvant setting. Direct comparisons with tamoxifen, as well as switching after several years from tamoxifen to an aromatase inhibitor, are strategies under evaluation. Early results from one of these trials evaluating anastrozole (the Arimidex, Tamoxifen, Alone or in Combination [ATAC] trial) has reported a reduced relapse rate after a median follow-up of 3 years in favour of anastrozole. However, this was at the expense of accelerated bone loss, and strategies to minimise this side effect of aromatase inhibitors are under investigation. Although many studies have indicated that bisphosphonates prevent the development of metastatic bone disease in animals, the clinical role of prophylactic bisphosphonates in early breast cancer is not clearly defined. Three studies with oral clodronate have been published, two of them indicating a protective effect on the development of bone metastases and improved survival, and one suggesting a disadvantage to the use of adjuvant clodronate. Further large adjuvant trials with clodronate and zoledronic acid are in progress. Adjuvant bisphosphonates also have been found to reduce bone loss associated with cancer treatments and preserve skeletal health. It may be possible to replace the current oral regimens for prevention of bone loss with a single annual infusion of the highly potent bisphosphonate zoledronic acid.

Update on clinical role of tamoxifen

PURPOSE OF REVIEW

Breast cancer is the most common malignancy amongst women in the United States and decreased mortality over the past decade has been attributed to a combination of screening and adjuvant therapies. There has been a resurgence of interest in hormonal therapies and this article discusses the clinical status of tamoxifen in the context of emerging alternative agents for treatment and prevention of breast cancer.

RECENT FINDINGS

Tamoxifen has served as a prototype for the development of selective estrogen receptor modulators at the laboratory-clinical interface. Molecular technologies have permitted elucidation of mechanisms for tissue specific action and led to newer selective estrogen receptor modulators with potentially greater antitumour efficacy and attenuated uterotrophic profile. Publications over the past 12 months have emphasized the risks of thromboembolism and endometrial carcinoma associated with tamoxifen use which has accelerated application of other hormonal agents for treatment of advanced disease and as neoadjuvant therapy. This article reviews the current role of tamoxifen in the treatment of early and advanced breast cancer together with its potential for chemoprevention. Models for quantitative risk assessment are being developed to identify women for whom chemoprotection is justified.

SUMMARY

Recent data showing a survival advantage for the aromatase inhibitor letrozole compared with tamoxifen in the advanced setting and improvement in disease-free survival for the aromatase inhibitor anastrozole versus tamoxifen as adjuvant treatment may herald a major shift in standard first-line endocrine therapies for both advanced and early disease and ultimately chemoprevention of breast cancer. Other agents including newer SERMs and pure antiestrogens are undergoing phase III clinical trials and future endocrine and biological therapies are likely to include more selective and targeted therapies, which may be efficacious in both hormone-sensitive and receptor-negative disease.

Aromatase inhibitors in prevention--data from the ATAC (arimidex, tamoxifen alone or in combination) trial and the design of IBIS-II (the second International Breast Cancer Intervention Study)

Current prevention trials have shown that tamoxifen can reduce the incidence of breast cancer by about 30%-40% in high-risk women, but that the risk of thromboembolic disease and endometrial cancer are increased about twofold. An alternative approach for postmenopausal women is to use an aromatase inhibitor to reduce oestrogen to very low levels. Data from the ATAC adjuvant trial indicate that the aromatase inhibitor anastrozole is more effective than tamoxifen in reducing recurrence and preventing new contralateral tumours, and also has a more favourable side-effect profile. This has led us to launch a new prevention trial--IBIS-II--in 6,000 high-risk postmenopausal women comparing anastrozole against placebo. A parallel trial will compare anastrozole against tamoxifen in 4,000 women with locally excised DCIS.

Prevention of breast cancer using SERMs and aromatase inhibitors

Breast cancer is one of the most common cancers of women in the Western world. Despite modest achievements in the treatment of this disease, there is a substantial unmet medical need to reduce the occurrence of new breast cancers. In several prospective, placebo-controlled trials, the antiestrogen tamoxifen has been shown to reduce the incidence of both invasive cancer and preinvasive breast lesions. Meanwhile, numerous other selective estrogen receptor modulators (SERMs) are being developed and trials comparing tamoxifen to these agents are ongoing. The goal of these studies is not only to show superior chemopreventive efficacy of the newer SERMs, but also an improved side-effect profile. The proof-of-principle demonstrated with tamoxifen suggests that strategies inhibiting estrogen are a logical way forward in breast cancer prevention. Aromatase inhibitors, which antagonize estrogen by blocking its synthesis from androgens, offer an alternative way of preventing the effects of estrogen and its metabolites on the breast. In this paper, the available data on SERMs including tamoxifen and raloxifene in breast cancer prevention and the data pointing to the efficacy of aromatase inhibitors in this setting are outlined.

Is there still a role for neoadjuvant therapy in breast cancer?

The role of neoadjuvant chemotherapy in locally advanced breast cancer is firmly established. There is now also an emerging role for neoadjuvant systemic therapy in the treatment of operable breast cancer. There is good evidence that the chances of breast conserving surgery can be increased with this approach and results of randomised studies indicate that survival is at least as good with neoadjuvant as with adjuvant chemotherapy. Similar clinical data are emerging with neoadjuvant endocrine therapy. For the future, there are important potential advantages in having an in vivo measure of chemosensitivity rather than blindly treating micrometastatic disease in the adjuvant setting. Clinical response to neoadjuvant treatment, and in particular complete pathological response, are predictors of subsequent outcome. Pathological involvement of axillary nodes following neoadjuvant therapy portends a poor prognosis. The potential for biological surrogate markers of response to predict for long-term outcome may allow individualisation of systemic treatment and the rapid assessment of new drugs in early breast cancer.

A stochastic economic evaluation of letrozole versus tamoxifen as a first-line hormonal therapy: for advanced breast cancer in postmenopausal patients

BACKGROUND

Letrozole is a third-generation aromatase inhibitor that is a feasible alternative to tamoxifen as a first-line hormonal therapy for patients with advanced breast cancer.

OBJECTIVE

This paper presents the results of an economic evaluation comparing letrozole and tamoxifen as first-line hormonal therapies in postmenopausal women diagnosed with advanced breast cancer.

PERSPECTIVE

UK National Health Service.

DESIGN

A decision model (Markov process) was built describing possible patient pathways from the point of diagnosis to death. The model was populated using patient-specific clinical trial data, data from the existing literature, and expert opinion. Stochastic analyses of the model were undertaken, whereby the majority of the input parameters were described as probability distributions to represent the uncertainty about their true value. Costs were presented in year 2000 values.

RESULTS

The baseline results showed that letrozole is a cost-effective alternative to tamoxifen with a mean incremental cost per life-year gained of pound 2342, whilst the incremental cost increases to just over pound 10,000 at the 95th percentile of the cost-effectiveness range (2000 values).

CONCLUSIONS

The results of the economic analysis indicate that letrozole is a cost-effective alternative first-line therapy compared with tamoxifen for postmenopausal women with advanced breast cancer, achieving additional life-years with a modest increase in costs.

Double-blind randomised trial comparing the non-steroidal aromatase inhibitors letrozole and fadrozole in postmenopausal women with advanced breast cancer

BACKGROUND

To compare the efficacy, safety and tolerability of letrozole, an advanced non-steroidal aromatase inhibitor, and fadrozole hydrochloride, an older-generation drug in this class, we conducted a randomised double-blind trial in postmenopausal women with advanced breast cancer.

PATIENTS AND METHODS

One hundred and fifty-seven postmenopausal women with advanced breast cancer were enrolled and randomly assigned to receive letrozole or fadrozole in a multicentre, randomised double-blind trial in Japan. One hundred and fifty-four eligible patients were treated with either letrozole 1.0 mg once daily (n = 77) or fadrozole 1.0 mg twice daily (n = 77), for a minimum of 8 weeks.

RESULTS

Letrozole showed a significantly higher overall objective response rate [complete response (CR) + partial response (PR)] than fadrozole (31.2% and 13.0%, respectively; P = 0.011, Fisher's exact test). Clinical benefits defined as CR, PR and stable disease (no change in status for more than 24 weeks) were also higher in patients treated with letrozole (50.6%) than fadrozole (35.1%). Letrozole was significantly superior to fadrozole in terms of the dominant lesion in soft tissue, bone and viscera (P = 0.011, stratified Mantel-Haenszel test). Median time to progression was 211 days in the letrozole group and 113 days in the fadrozole group with no significant difference (P = 0.175, log-rank test). Letrozole markedly reduced the estradiol, estrone and estrone sulfate levels in peripheral blood within 4 weeks. The suppressive effect of fadrozole on these hormone levels was insufficient. Adverse drug reactions were observed in 35.9% of the patients treated with letrozole and in 39.5% of those treated with fadrozole with no significant difference between the two groups (P = 0.74, Fisher's exact test). Most of the adverse drug reactions were rated as grade 1 or 2.

CONCLUSIONS

The results show letrozole at a dose of 1.0 mg once daily to be more effective in treating postmenopausal women with advanced breast cancer than fadrozole at 1.0 mg twice daily, with similar safety and tolerability profiles.

Safety issues surrounding the use of aromatase inhibitors in breast cancer

Third generation aromatase inhibitors (AIs) are now established therapy in advanced oestrogen receptor (ER)-positive breast cancer. As the use of AIs expands to include adjuvant treatment of early breast cancer and breast cancer prevention, tolerability and effects on other organs such as bone will become as important as the antitumour properties of the drugs. In direct comparisons with tamoxifen, AIs have a better toxicity profile with fewer patients stopping therapy because of drug-related side effects. There is a lower incidence of thromboembolic events and vaginal bleeding compared with tamoxifen. Although published information about the side effects of AIs is scarce, it is likely that they will have adverse effects on bone and possibly also on lipid metabolism. Subprotocols of ongoing adjuvant trials are investigating these effects. It is likely that the choice of which third generation AI to use will be largely determined by its tolerability and safety profile, since it is likely that the currently available drugs have similar efficacy.

Anti-tumor effects of letrozole

The use of drugs, which inhibit estrogen biosynthesis, is an attractive treatment for postmenopausal women with hormone-dependent breast cancer. Estrogen deprivation is most specifically achieved using inhibitors which block the last stage in the biosynthetic sequence, i.e., the conversion of androgens to estrogens by the aromatase enzyme. Recently, a new generation of aromatase inhibitors has been developed. Among these, letrozole (Femara) appears to be the most potent. When given orally in milligram amounts per day to postmenopausal women, the drug almost totally inhibits peripheral aromatase and causes a marked reduction in circulating estrogens to levels that are often undetectable in conventional assays. Similarly, neoadjuvant studies demonstrate that letrozole substantially inhibits aromatase activity in both malignant and nonmalignant breast tissues, and markedly suppresses endogenous estrogens within the breast cancers. These studies also illustrate anti-estrogenic and anti-proliferative effects of letrozole in estrogen receptor (ER)-rich tumors. Thus, tumor expression of progesterone receptors and the cell-cycle marker Ki67 is significantly and consistently reduced with treatment. Additionally, clear pathological responses as evidenced by decreased cellularity and increased fibrosis are seen in the majority of cases. These results translated into clinical benefit in a series of 24 breast cancers treated neoadjuvantly with letrozole (either 2.5 or 10 mg): tumor volume reductions > 25% were observed in 23 women, and > 50% reductions in 18 patients. Pathological and clinical effects are seen much more consistently than with tamoxifen. Thus, in a multicenter randomized trial of letrozole vs. tamoxifen (PE 024), clinical study outcomes were superior for letrozole in comparison with tamoxifen with regard to overall tumor response and an increase in the proportion of patients treated by breast conserving surgery. Letrozole has also been used in advanced breast cancer, both as second-line hormone treatment following tamoxifen failure, and more recently as first-line therapy. Trials of second-line treatment in which letrozole has been compared with either older aromatase inhibitors or progestins have shown equivalent or superior clinical activity and improved tolerability favoring letrozole. In first-line comparison with tamoxifen in metastatic disease, a phase III trial of over 900 postmenopausal women showed letrozole to be significantly better than tamoxifen in terms of overall tumor response rates, clinical benefit, and time to treatment failure. In summary, letrozole is an exceptionally potent and specific endocrine agent. In patients with ER-rich tumors, high rates of pathological and clinical response have been documented, and large phase III trials against established treatments such as tamoxifen and progestin suggest superior (or at least equivalent) clinical efficacy. Letrozole is a drug of immense potential and in the future is likely to occupy a central role in the management of postmenopausal women with hormone-dependent breast cancer.

Strategies for improving quality of life in older patients with metastatic breast cancer

Given both the increase in the mean age of the population of Western countries and the high incidence of breast cancer beyond the age of 65 years, it is evident that breast cancer in older women will be a very common problem for the medical oncologist. Metastatic breast cancer is still not amenable to a cure; therefore quality of life during therapy is an important issue, which until recently has been poorly investigated. Similarly, despite recent advances in breast cancer therapy, physicians have been reluctant to enrol older patients in clinical trials, and there is a lack of data regarding this population. This review focuses on quality-of-life issues during metastatic breast cancer treatment in geriatric patients, comparing the standard therapeutic options and newer approaches. Although first-line endocrine therapy with tamoxifen remains a standard treatment, the newer third-generation aromatase inhibitors provide similar or better efficacy with fewer adverse effects and a better quality of life. It has been a common belief that chemotherapy impairs quality of life, but recent studies in advanced breast cancer have shown that this therapy has a positive effect on quality of life, at least in responders. Consequently, chemotherapy should not be denied to elderly patients with metastatic breast cancer, provided a prior geriatric assessment is performed to evaluate the risk-benefit ratio. New chemotherapy strategies, such as the taxanes and orally administered chemotherapy, represent a very attractive alternative for a better quality of life in elderly patients with metastatic breast cancer.

Aromatase inhibitors in breast cancer: an update

BACKGROUND

Tamoxifen has been the endocrine treatment of choice for patients with breast cancer. The development of selective aromatase inhibitors has offered an alternative management approach for patients in whom a hormonal approach is indicated.

METHODS

The authors reviewed reports in which aromatase inhibitors were compared with tamoxifen for the treatment of metastatic disease, as well as information pertinent to their use as adjuvant therapy.

RESULTS

Both nonsteroidal (anastrozole and letrozole) and steroidal (exemestane) aromatase inhibitors for metastatic disease appear to provide superior efficacy and a better toxicity profile in first- and second-line treatment of metastatic disease than tamoxifen. Early results from the ATAC trial suggest anastrozole is superior to tamoxifen for disease-free survival, particularly in receptor-positive patients, and in reducing the incidence of contralateral breast cancer.

CONCLUSIONS

Aromatase inhibitors have important roles in optimal management of postmenopausal patients with hormone-responsive metastases in both the adjuvant and advanced-disease settings.

An overview of the pharmacology and pharmacokinetics of the newer generation aromatase inhibitors anastrozole, letrozole, and exemestane

BACKGROUND

The newer generation, nonsteroidal aromatase inhibitors (AIs) anastrozole and letrozole have shown superior efficacy compared with tamoxifen as first-line treatments and compared with megestrol acetate as second-line therapy in postmenopausal women with advanced breast carcinoma. In an open-label, Phase II trial, it was reported that exemestane showed numerical superiority compared with tamoxifen for objective response and clinical benefit. Because these agents ultimately may be administered for periods of up to 5 years in the adjuvant setting, it is of increasing importance to assess their tolerability and pharmacologic profiles.

METHODS

In the absence of data from direct clinical comparisons, the published literature was reviewed for the clinical pharmacology, pharmacokinetic characteristics, and selectivity profiles of anastrozole, letrozole, and exemestane.

RESULTS

At clinically administered doses, the plasma half-lives of anastrozole (1 mg once daily), letrozole (2.5 mg once daily), and exemestane (25 mg once daily) were 41-48 hours, 2-4 days, and 27 hours, respectively. The time to steady-state plasma levels was 7 days for both anastrozole and exemestane and 60 days for letrozole. Androgenic side effects have been reported only with exemestane. Anastrozole treatment had no impact on plasma lipid levels, whereas both letrozole and exemestane had an unfavorable effect on plasma lipid levels. In indirect comparisons, anastrozole showed the highest degree of selectivity compared with letrozole and exemestane in terms of a lack of effect on adrenosteroidogenesis.

CONCLUSIONS

All three AIs demonstrated clinical efficacy over preexisting treatments. However, there were differences in terms of pharmacokinetics and effects on lipid levels and adrenosteroidogenesis. The long-term clinical significance of these differences remains to be elucidated.

Sequencing of hormonal therapy in breast cancer

Hormonal therapy plays an integral role in the management of the majority of women with breast cancer who can be considered to have hormone-dependent breast cancer because of the presence of the molecular predictive markers, estrogen receptor and progesterone receptor. Numerous hormonal agents are available from multiple classes of drugs, including selective estrogen receptor modulators, aromatase inhibitors, progestins, androgens, and luteinizing hormone-releasing hormone analogues. Multiple clinical trials involving these agents have been conducted which permit an evidence-based approach to the development of a sequencing strategy for treatment of women with breast cancer.

Systemic therapy

The systemic treatment of breast cancer is a moving target, reflected by the continuous update of treatment guidelines. Chemotherapy regimens, including the adjuvant role of taxanes and preoperative systemic therapy, continue to be optimized. A major challenge facing researchers and clinicians is how to improve the therapeutic index of present and future therapies, identify patients most likely to benefit from the proposed intervention, and avoid treating those who would be exposed to potential toxicities with minimal gain. Anti-estrogens are a prime example of a targeted therapy with a high therapeutic index. Data are now available on aromatase inhibitors in the adjuvant setting and pure antiestrogens in metastatic disease. The role of targeted antihuman epidermal growth factor receptor 2 therapy in the adjuvant setting is being actively investigated, but this is complicated by the inadequate standardization of human epidermal growth factor receptor 2 expression assays used in clinical practice. A long overdue revision of the breast cancer staging system becomes effective in January 2003, bringing it more in line with current standards of care and facilitating data collection for future outcome analysis of therapeutic interventions. These and other important developments since 2001 are examined in this review.

Epirubicin/docetaxel regimen in progressive breast cancer-a phase II study

The purpose of this investigation was to evaluate the efficacy and toxicity of 6 months' treatment with the combination of epirubicin and docetaxel in metastatic breast cancer. Thirty-eight women (mean age 51 years, range 35-72) with metastatic breast cancer were treated with a regimen of epirubicin 75 mg/m and docetaxel 75 mg/m every 3 weeks, given 4 times if progression was seen upon evaluation after 4 courses or 8 times in responding/stable patients. The patients received 285 cycles of combination treatment and two treatments with docetaxel or epirubicin alone. When neutropenia with fever was observed, further cycles were given with dose reduction. The median cumulative docetaxel dose was 462 mg/m (range 199-600) and that of epirubicin 476 mg/m (range 199-740). The overall response rate was 54% (95% CI 37-71), with a median duration of response of 14.8 months (95% CI 8.8-27.8). Median time to progression was 12 months, median survival 26 months. Neutropenia below 0.5 x 10 /l occurred following 113 (39%) of the total of 285 cycles given; 21 patients (55%) were hospitalized for febrile neutropenia. We conclude that dose tailoring is required in treatment with an epirubicin and docetaxel regimen to avoid grade 3/4 adverse effects in a significant number of patients treated for metastatic breast cancer.

Anti-oestrogenic prevention of breast cancer--the make or break point

Clinical trials have shown that giving anti-oestrogens to healthy women can reduce the early incidence of breast cancer by approximately 40%. However, the large numbers of women treated, compared with the few who get breast cancer, together with the not insignificant toxicity and the unknown long-term clinical benefits and risks, makes this strategy of prevention versus treatment precarious. So how can we improve the odds for the successful use of endocrine chemoprevention?

Efficacy and economics of hormonal therapies for advanced breast cancer

Breast cancer is a leading cause of cancer-related mortality among postmenopausal women in the US, and the economic burden of breast cancer care comprises a large percentage of the healthcare budget. Hormonal therapies have a proven place in the management of advanced breast cancer. This type of therapy is more likely to be used in older, compared with younger, women, because tumours in older women are more likely to express estrogen and progesterone receptors. While it is difficult to measure the costs of cancer care because of variation in extent and duration of treatment, treatment-related costs including costs of hormonal agents used for advanced disease account for a relatively small component of the overall costs. Newer hormonal regimens such as the new third generation nonsteroidal (letrozole, anastrozole) and steroidal (exemestane) aromatase inhibitors have shown improved clinical efficacy compared with standard regimens such as megestrol and tamoxifen in the metastatic setting in terms of objective responses or time to tumour progression. In addition the newer agents have improved toxicity profiles. Cost analyses of the newer aromatase inhibitors (anastrozole and letrozole), compared with megestrol, show an optimistic outlook for these agents. Additional work needs to be done looking at a comparison of the efficacy and costs of the aromatase inhibitors relative to the currently recommended hormonal treatments used for women with metastatic breast cancer.

Anastrozole in the management of breast cancer

Anastrozole (Arimidex, AstraZeneca) is a third-generation aromatase inhibitor which rapidly reduces oestradiol concentrations to below detectable levels. It is both potent and selective for the aromatase enzyme, with near-maximal suppression of serum oestrogens occurring at the clinical dose of 1 mg/day in postmenopausal women with advanced breast cancer. Anastrozole has also been shown to be a potent suppressor of intratumoural oestrogens, with responses comparable to those in serum. The results of two large, identically designed, randomised trials in postmenopausal women with advanced breast cancer who had progressed on tamoxifen showed that oral anastrozole 1 mg/day produced a statistically significant survival advantage over megestrol acetate 40 mg q.i.d. The median duration of survival was 26.7 months for anastrozole versus 22.5 months for megestrol acetate. Anastrozole was as well-tolerated as megestrol acetate, while weight gain was significantly increased in the megestrol acetate group compared with the anastrozole group. In another Phase III clinical trial involving 1021 postmenopausal women with advanced breast cancer, anastrozole showed a statistically significant advantage over tamoxifen in median time to progression in a combined analysis of 611 patients who were known to be oestrogen receptor- or progesterone receptor-positive. Anastrozole was as well-tolerated as tamoxifen, with a low rate of withdrawals (2%) due to drug-related adverse events. In addition, anastrozole was associated with fewer thromboembolic events and episodes of vaginal bleeding than tamoxifen. For women with hormone receptor-positive tumours who progress on tamoxifen, anastrozole is superior to megestrol acetate. In addition, anastrozole is a reasonable alternative to tamoxifen for first-line endocrine therapy of advanced breast cancer. Recent data confirm an emerging role for anastrozole as adjuvant therapy for primary breast cancer in postmenopausal patients. Anastrozole is also being investigated in the neoadjuvant setting.

Relationship of Serum HER-2/neu and Serum CA 15-3 in Patients with Metastatic Breast Cancer

Background: Serum HER-2/neu antigen concentrations have been reported to correlate with increased tumor volume in patients with breast cancer. We measured serum CA 15-3, a surrogate marker of disease burden, and correlated serum CA 15-3 with serum HER-2/neu and analyzed the association of both markers with clinical outcomes.

Methods: Pretreatment serum samples from 566 patients were retrospectively analyzed from 2 phase III clinical trials of estrogen receptor-positive (ER+), ER−/progesterone receptor-positive, or ER status unknown metastatic breast cancer patients randomized in two similar studies to receive second-line hormone therapy with either megestrol acetate or an aromatase inhibitor (fadrozole). The extracellular domain of the HER-2/neu (c-erbB-2) oncogene and serum CA 15-3 were measured by ELISA on the Bayer Immuno 1.

Results: Serum HER-2/neu protein was increased in 168 patients (30%), and CA 15-3 was increased in 337 (60%) patients. Serum CA 15-3 and HER-2/neu were weakly correlated (r = 0.39; P <0.0001). The clinical benefit (complete responses plus partial responses plus stable disease) of endocrine therapy was significantly lower in patients with increased serum HER-2/neu. When adjusted for serum HER-2/neu, serum CA 15-3 was not predictive of response rates. The median time to progression was shorter in patients with increased serum HER-2/neu (89 days) compared with patients with normal serum HER-2/neu (176 days). Survival was significantly shorter in patients with increased serum HER-2/neu (513 vs 869 days; P <0.0001) or increased serum CA 15-3 (689 vs 939 days; P <0.0001). This observation was confirmed by multivariate analysis.

Conclusions: Serum HER-2/neu is a significant independent predictive and prognostic factor in hormone receptor-positive metastatic breast cancer, even when adjusted for tumor burden as measured by CA 15-3. The combination of increased serum HER-2/neu and increased serum CA 15-3 predicts a worse prognosis than does increased CA 15-3 alone.

Tamoxifen ("Nolvadex"): a review

Tamoxifen has been used in the management of breast cancer for over 30 years. Since its introduction for the treatment of advanced breast cancer, its indications have increased to include the treatment of early breast cancer, ductal carcinoma in situ, and more recently for breast cancer chemoprevention. Tamoxifen has a good tolerability profile and moreover, unlike many other endocrine therapies, it is efficacious in both pre- and postmenopausal women. It is the combination of efficacy and tolerability that allows tamoxifen to maintain its position as the hormonal treatment of choice for most patients with oestrogen-receptor positive breast cancer. Ongoing studies will provide further information about the optimal duration of tamoxifen therapy and how it compares with the newer aromatase inhibitors.

Adaptive mechanisms induced by long-term estrogen deprivation in breast cancer cells

Clinical observations suggest that human breast tumors can adapt in response to endocrine therapy by developing hypersensitivity to estradiol. To understand the mechanisms responsible, we examined estrogenic stimulation of cell proliferation in a model system and provided evidence that long-term deprivation of estradiol causes adaptive hypersensitivity. The enhanced responses to estradiol do not involve mechanisms acting at the level of transcription of estrogen regulated genes. We found no evidence of hypersensitivity when examining the effects of estradiol on regulation of c-myc, pS2, progesterone receptor, several ER reporter genes or c-myb in hypersensitive cells. On the other hand, deprivation of breast cells long term was found to up-regulate a separate pathway whereby the estrogen receptor co-opts a classical growth factor pathway and induces rapid non-genomic effects. Through this pathway, estradiol caused rapid activation of mitogen-activated protein (MAP) kinase. In exploring the mechanisms mediating this event, we found that estradiol binds to cell membrane associated estrogen receptors and causes phosphorylation of Shc, an adaptor protein usually involved in growth factor signaling pathways. ERalpha was found to complex with Shc under these conditions. In turn, Shc bound Grb-2 and Sos which resulted in the activation of MAP kinase. The pure antiestrogen, ICI 182,780, blocked several steps in the rapidly responding ER alpha, Shc, MAP kinase pathway. These non-genomic effects of estradiol produced biologic effects by activating Elk and by inducing morphologic changes in cell membranes. Using confocal microscopy, we demonstrated that estradiol caused a rapid alteration in membrane ruffling, the formation of pseudopodia and translocation of ER alpha to regions contiguous with the cell membrane. These morphologic effects could be blocked with a pure anti-estrogen. We conclude that long-term estradiol deprived cells utilize both genomic (transcriptional) and rapid, non-genomic estradiol induced pathways. We postulate that synergy between these two pathways acting at the level of the cell cycle is responsible for adaptive hypersensitivity.

Aromatase overexpression enhances the stimulatory effects of adrenal androgens on MCF7 breast cancer cells

The intratumoral conversion of adrenal androgens into estrogens by the aromatase enzyme complex may be an important mechanism of autocrine stimulation in hormone-dependent breast tumor. The effects of estrogens on tumor development are mediated by the activity of estrogen receptor alpha that induces gene expression and cell proliferation. Thus, estrogen biosynthesis 'in situ' and/or estrogen receptor action are the main targets of endocrine treatment in endocrine-dependent breast carcinoma. In the present study we demonstrate that three major adrenal androgens, dehydroepiandrosterone, 5-androstene-3beta, 17beta-diol and 4-androstene 3,17-dione, all acquire an estradiol-like biological efficacy in aromatase transfected MCF7 breast cancer cells. Our results suggest that in postmenopausal women aromatase inhibitors might be considered as an adjuvant approach to the treatment of hormone-dependent breast tumors that overexpress aromatase.

Aromatase inhibitors and inactivators for breast cancer therapy

Aromatase inhibitors and inactivators are increasingly important to the therapy of advanced breast cancer in postmenopausal women. These compounds are also currently being evaluated in the adjuvant setting and may have potential in breast cancer prevention. In addition to the recent clinical results, experimental research with development of aromatase 'knockout' mice as well as certain clinical observations in individuals lacking this enzyme have deepened our understanding of estrogens outside of the field of reproduction. Such information should help us to further develop this type of therapy in breast cancer and, in particular, extend our understanding of the lack of complete cross-resistance between aromatase inhibitors and inactivators. Clinically, third-generation aromatase inhibitors and inactivators have shown superiority compared with conventional treatment in advanced postmenopausal breast cancer with respect to second-line (tamoxifen failures) as well as first-line therapy. The fact that tamoxifen is noncurative in metastatic disease but improves long-term survival in the adjuvant setting suggests that even modest improvements in therapy of advanced disease may be translated into survival benefits in patients with early disease. In addition, these novel compounds with lack of complete cross-resistance extend the scope of using sequential treatment options to maximise the duration of optimal endocrine therapy in metastatic breast cancer disease.

Chemoprevention of breast cancer: implications for postmenopausal women

Estrogen administration is associated with reduction in perimenopausal symptoms and the risk for several conditions affecting postmenopausal women. As estrogen administration also increases the risk for breast cancer, a common dilemma facing many women and their physicians is whether to use estrogen replacement therapy (ERT), a selective estrogen receptor modulator (SERM) that antagonises estrogenic effects in breast tissue but retains some estrogen agonist properties in other organs, or neither. For women with average to moderate risk of breast cancer and with perimenopausal symptoms, ERT may be the best short-term choice. For very high-risk women (>1% per year) with menopausal symptoms, alternatives to ERT might be offered and tried first. A diagnosis of ductal carcinoma in situ or invasive breast cancer within the last 2 to 5 years should be considered a relative contraindication for ERT unless the tumour was estrogen receptor negative. High-risk women without menopausal symptoms are the best candidates for the only currently approved drug for breast cancer risk reduction, tamoxifen. Although the drug is approved for women with a 5-year risk of breast cancer > or = 1.7% (0.34% per year), postmenopausal women most likely to experience a favourable benefit/risk ratio are those with a Gail estimated risk of >0.5% per year without a uterus or >1% per year if they retain their uterus. Tamoxifen should not be used in women with prior history of thromboembolic or precancerous uterine conditions. Tamoxifen is often used in Europe in conjunction with transdermal ERT in hysterectomised women without obvious loss of efficacy or increased risk of thromboembolism. Raloxifene is a second generation SERM with estrogen-like agonist effects on bone but with less uterine estrogen agonist activity than tamoxifen. Raloxifene may have less potent breast antiestrogenic effects than tamoxifen, particularly in a moderate- to high-estrogen environment. Raloxifene is approved for use in reducing risk of osteoporosis, but not breast cancer. Whether it is as effective as tamoxifen in reducing breast cancer risk in postmenopausal women is the subject of a current trial. All women regardless of breast cancer risk are advised to employ nonpharmacological risk reduction measures, including normalisation of bodyweight, exercise, adequate calcium and vitamin D intake, and avoidance of smoking and alcohol. The preventive options are best weighed during an individualised consultation where a woman's menopausal symptoms and risk for breast cancer and other diseases can be examined, and the options for improving postmenopausal health can be discussed.

Tamoxifen resistant and refractory breast cancer: the value of aromatase inhibitors

Tamoxifen has dominated endocrine treatment of breast cancer for over two decades. It is useful in metastatic breast cancer, adjuvant therapy, preoperative treatment, ductal carcinoma-in-situ and chemoprevention. However, breast cancer may be refractory to tamoxifen or develop resistance to it with ongoing treatment. This resistance involves several mechanisms including receptor mutation causing 'estrogen hypersensitivity' and an increasing agonist effect of tamoxifen. Megestrol (megestrol acetate), in North America, and aminoglutethimide, in Europe, have been the traditional second line therapies after tamoxifen in advanced breast cancer. Aromatase (estrogen synthetase) inhibitors are a logical alternative to tamoxifen to antagonise the effects of estrogen on breast cancer. The third-generation non-steroidal aromatase inhibitors anastrozole, letrozole and vorozole, and the steroidal inhibitor exemestane, have been studied after tamoxifen versus either megestrol or aminoglutethimide. They showed enhanced efficacy and significantly superior toxicity profiles. Compliance with the inhibitors was also significantly better than with the traditional treatments. Aromatase inhibitors have most recently been shown to be superior to tamoxifen as initial therapy and are being extensively tested in the adjuvant setting after, or instead of, tamoxifen. Pilot studies of chemoprevention are also being undertaken. The aromatase inhibitors are an important new addition to the armamentarium of breast cancer therapy.

Breast cancer chemoprevention: current challenges and a look toward the future

There is a need to develop new prevention agents for breast cancer risk reduction that would have fewer side effects than the approved agent, tamoxifen, and/or would be effective in preventing estrogen receptor-negative or tamoxifen-resistant, estrogen receptor-positive breast cancers. There also is a need to improve the accuracy of present risk assessment models and to incorporate tissue-based biomarkers to supplement risk prediction tools. Candidate risk biomarkers include the serum hormones insulin-like growth factor-1 and its binding protein-3, mammographic breast density, nipple aspirate fluid production, and breast tissue evidence of proliferative breast disease (intraepithelial neoplasia). A variety of techniques have been developed to randomly sample breast tissue to detect precancerous changes and/or detect modulation of proliferation in response to a prevention agent. Based on molecular abnormalities observed in breast intraepithelial neoplasia, a number of drug classes and combinations are suggested as potential chemoprevention approaches. Clinical trial models have been developed to select the appropriate drug dose for subsequent biomarker modulation chemoprevention trials in which the use of surrogate endpoint biomarkers as indicators of efficacy is being explored. If these biomarkers can be validated and shown to reliably predict and monitor response in phase I/II prevention trials, and if favorable modulation is correlated with subsequent decreased cancer incidence, biomarkers may replace cancer incidence as the endpoint in future phase III trials, dramatically reducing the time and expense associated with new prevention drug development.

The evolution of tamoxifen therapy in breast cancer: selective oestrogen-receptor modulators and downregulators

Tamoxifen is the most widely used hormonal treatment for all stages of breast cancer and has been approved for the prevention of breast cancer in high-risk women. The observation that tamoxifen acts as an antioestrogen on the breast but has paradoxical oestrogenic effects on bones and lipids heralded the development of the selective oestrogen-receptor modulators (SERM). Raloxifene, another of these drugs, is being used to prevent osteoporosis in postmenopausal women, but it seems, like tamoxifen, to prevent breast cancer. The molecular basis for these target-site-specific actions remains unclear but may involve the relative expressions of coregulatory proteins in target tissues. Several new SERM agents are in clinical development in an attempt to decrease the unwanted effects. Furthermore, two different classes of hormonal agents, the aromatase inhibitors and oestrogen-receptor downregulators, which have no oestrogen-like properties at any site, are promising new treatments for breast cancer.

Medical management of breast cancer: today and tomorrow

The medical management of invasive breast cancer has evolved based on the recognition that surgery alone was associated with few long-term cures. This Update will review the current status of breast cancer medical management in three areas: prevention in individuals with an elevated risk, adjuvant (postoperative) treatment of early breast cancer, and treatment principles in metastatic disease. Tamoxifen has emerged as a promising agent in the treatment of women at an increased risk for breast cancer and in those with in situ disease. However, the risks of treatment must be carefully weighed against the benefits in these cohorts of women with an excellent overall prognosis. This same principle can be applied to the use of adjuvant treatment in early invasive breast cancer, where the goal is cure. Adjuvant polychemotherapy is recommended in women considered at high-risk for relapse and death. In addition, women with hormone-sensitive breast cancer are offered adjuvant taxmoxifen. Nonetheless, there are some patients with low-risk disease or those with significant co-morbidities that are unlikely to benefit from adjuvant therapies and likely to sustain toxicities. The treatment goal in metastatic breast cancer is focused on palliation of symptoms as fewer than 10% of such patients achieve 5-year survival. However, novel targeted therapies are changing the treatment armamentarium and hold great promise. These new directions of treatment will be discussed as well as areas of controversy.

Antiaromatase agents: evolving role in adjuvant therapy

The goal of adjuvant hormonal therapy is to prevent breast cancer recurrence. Standard therapy with tamoxifen has shown great value in the adjuvant setting; however, its tolerability profile can render it unsuitable for some patients. The aromatase inactivator, exemestane, and the 2 aromatase inhibitors, letrozole and anastrozole, have been shown to be equivalent or superior to tamoxifen with respect to multiple endpoints in patients with metastatic breast cancer. With tolerability profiles that are similar to, and in many cases, more acceptable than that of tamoxifen, and efficacy potentially superior to tamoxifen, studies using the antiaromatase agents as adjuvant therapy are currently ongoing. These trials will answer some important questions, such as the order in which adjuvant hormonal therapies are selected to maximize efficacy, whether the antiaromatase agents show improved tolerability, and whether combination therapy is more effective than monotherapy.

Anti-aromatase agents in the treatment and prevention of breast cancer

Anti-aromatase agents now have a central role in the management of breast cancer in postmenopausal women; they are superior to megestrol acetate as second-line therapy and to tamoxifen for initial therapy of metastatic disease. They also are highly active as neoadjuvant therapy. Two classes of anti-aromatase agents are available: steroidal (eg, exemestane) and nonsteroidal (eg, anastrozole, letrozole). Although both types of agents act on the aromatase enzyme, they do so by different mechanisms and have different effects on cellular aromatase activity. Nonsteroidal agents are associated with increased aromatase enzyme content and steroidal agents are associated with decreased content. The increase in aromatase content seen with the nonsteroidal agents may in part explain the development of resistance with these agents and the ability of the steroidal agent exemestane to induce a response when nonsteroidal agents fail. Because the anti-aromatase agents almost completely eliminate endogenous estrogen production, they not only affect breast cancer tissues, but also may alter the function of other estrogen-responsive tissues. However, preclinical data show that the steroidal agent exemestane may actually improve bone and lipid metabolism. In addition, no increase in clinical fracture rate has been noted in women treated with exemestane in metastatic trials; the fracture risk has not yet been studied following prolonged exposure in healthy women. Exemestane associated beneficial effects on these end organs may be due to the steroidal nature of both the parent compound and its principal metabolite, 17-hydroexemestane. Similar benefits have not been reported with nonsteroidal antiaromatase agents. Based on their excellent activity in the metastatic setting, anti-aromatase agents are now being evaluated in the adjuvant setting and in pilot studies for chemoprevention. These studies will provide long-term data in healthy women and will help to differentiate anti-aromatase agents, in terms of their efficacy in the treatment of breast cancer and their effects on end organs.