Aromatase inhibitors as adjuvant therapy for postmenopausal patients with early stage breast cancer

Endocrine therapy of hormone receptor-positive breast tumors is widely used as palliative therapy for metastatic breast cancer and as adjuvant therapy for early stage breast cancer. Tamoxifen has been the definitive standard of hormonal therapies for the last 30 years because of its documented efficacy and reasonable safety profile. Based on encouraging results from trials utilizing the selective, third generation aromatase inhibitors (AIs) in metastatic breast cancer, a number of trials were designed to examine these agents as adjuvant therapies. Trials directly comparing AIs with tamoxifen have, to date, demonstrated superior disease-free-survival with AIs. Likewise, trials examining the use of AIs after tamoxifen have demonstrated better outcomes compared with tamoxifen alone. Additionally, letrozole has been demonstrated to result in superior disease-free-survival after 5 years of adjuvant tamoxifen, compared with no further therapy. In general, the AIs are tolerated at least as well as tamoxifen but decrease bone mineral density and increase osteoporosis due to their lack of estrogenic effects on bone. Based on the fact that AIs appear more effective at preventing contralateral breast cancers than tamoxifen, they are being examined as breast cancer preventives. Despite available data using the AIs as adjuvant therapies, many questions remain unanswered, and further trials will be needed to address these important issues.     

Safety considerations of adjuvant therapy in early breast cancer in postmenopausal women

Because of its proven efficacy profile based on long-term data, tamoxifen has been the standard adjuvant endocrine therapy for hormone-sensitive early breast cancer for the past 30 years. However, there is well-established evidence that long-term use of tamoxifen is associated with serious side effects. As adjuvant endocrine therapy is generally administered for long periods of time, the safety and tolerability of agents used in this setting are of particular importance. Due to their superior efficacy over tamoxifen, newer agents, such as the third-generation aromatase inhibitors (AIs), are already established therapies for the treatment of advanced breast cancer. In addition, recent trials indicate that the AI anastrozole ('Arimidex') has improved efficacy compared with tamoxifen in the adjuvant setting in postmenopausal women. The other third-generation AIs have reported disease-free survival benefits but not in the absence of prior treatment with tamoxifen; letrozole ('Femara') has been compared with placebo following 5 years of tamoxifen therapy and exemestane ('Aromasin') has been compared with tamoxifen following 2-3 years of prior treatment with tamoxifen. Long-term safety data show that anastrozole also has a more favorable overall safety profile compared with tamoxifen, particularly in terms of life-threatening events such as endometrial cancer and thromboembolism. Anastrozole alone, therefore, provides a new option for adjuvant therapy in postmenopausal women with hormone-receptor-positive early breast cancer. The AIs have differing pharmacological profiles, which may translate into dissimilar adverse event profiles in the adjuvant treatment setting, but patient follow-up in most trials is relatively short to make a valid comparison. It cannot, therefore, be assumed that all AIs will be equally well tolerated in the adjuvant setting. Further data on the long-term safety of AIs other than anastrozole are therefore required to allow overall risk:benefit assessments on these agents to be made.     

Adjuvant endocrine therapy for early breast cancer

Breast cancer is the most common cancer among women and about 80% of breast cancers express hormone receptors. Tamoxifen has been the most important form of adjuvant endocrine therapy over the last 25 years. The third generation aromatase inhibitors (AIs) are a new class of drugs challenging the central role of tamoxifen as adjuvant endocrine treatment in postmenopausal women with hormone receptor-positive breast cancer. Their effectiveness has been demonstrated in first line therapy as well in neoadjuvant setting with a statistically significant superiority over tamoxifen. Here we considered the role of adjuvant AIs in early stage breast cancer with an analysis reviewing the main adjuvant trials. We considered efficacy, side effects, optimal timing, duration of the therapy and whether specific subgroups may achieve particular benefit. In conclusion the upfront use of adjuvant anastrozole or letrozole is superior to tamoxifen with a good relative toxicity profile. Tamoxifen will continue to have a role where recurrence risk is low or if AI is poorly tolerated. Issues including the timing of administration (up-front or sequential), the duration of the therapy and the role of biomarkers such as PgR and HER2 in optimal selection remain unresolved.     

Recent advances in endocrine therapy for postmenopausal women with early breast cancer: implications for treatment and prevention.

BACKGROUND: In the treatment of advanced breast cancer, third-generation aromatase inhibitors (AIs) have shown superior efficacy and tolerability compared with tamoxifen and megestrol acetate, the previous standard endocrine therapies in the first- and second-line settings, respectively. AIs are now being assessed in the adjuvant and prevention settings. DESIGN: Literature review (PubMed search). RESULTS: Tamoxifen is currently the only endocrine option available for adjuvant therapy and chemoprevention in postmenopausal women. However, results from the ATAC ('Arimidex', Tamoxifen, Alone or in Combination) trial have shown anastrozole to be more effective than tamoxifen as adjuvant therapy for postmenopausal women with hormone-responsive early breast cancer. Other third-generation AIs, including letrozole and exemestane, are also being investigated as adjuvant therapies. In the chemoprevention setting, tamoxifen is the only available endocrine option for women at high risk of breast cancer but, given that these are healthy subjects, is associated with an unacceptable rate of adverse events. Raloxifene is being further assessed in the STAR (Study of Tamoxifen and Raloxifene) trial, while anastrozole is being evaluated in the second IBIS-II (International Breast Intervention Study II). CONCLUSIONS: AIs, in particular anastrozole, are set to change the way that early breast cancer is treated. Effective and better-tolerated endocrine alternatives for breast cancer prevention may become available in the future.     

Safely promoting breast-conserving surgery and preventing early relapses with an aromatase inhibitor

Neoadjuvant therapy improves patient outcomes substantially by increasing the rate of breast-conserving surgery. Following primary surgery, women with hormone-sensitive early breast cancer remain at risk for loco-regional and systemic recurrence. The most common relapse event, distant metastases, is associated with the poorest outcomes. As a neoadjuvant therapy, anastrozole, letrozole, and exemestane have been investigated in phase 3 studies and have shown efficacy in this setting. All three aromatase inhibitors (AIs) significantly improved the rate of breast-conserving surgery. As initial adjuvant therapy, the third-generation AIs anastrozole and letrozole more effectively reduce recurrence risk compared with tamoxifen following surgery, especially in the first 2 years, when the risk is greatest. Tamoxifen, once the standard initial therapy, is associated with improved disease-free survival but may be more effective at reducing loco-regional recurrence than distant metastases. Initial adjuvant letrozole therapy has also shown a pronounced reduction in the risk of distant metastases early on in the course of therapy. If AIs are not used upfront, sequential use of exemestane or anastrozole following tamoxifen provides greater protection against relapse than continuing on tamoxifen. Side effects associated with estrogen deprivation of AIs are less serious than those of tamoxifen and are easily managed. Various molecular markers are under study as surrogates to predict response to neoadjuvant therapy, which may in turn predict responsiveness to adjuvant therapy. Surgeons treating breast cancer patients and prescribing endocrine therapy should be aware of all treatment strategies, including neoadjuvant and adjuvant hormonal therapy, and inform their patients of the benefits and the potential side effects. Early and long-term-risk reduction with AI treatment should be discussed with patients, as should the management of common AI-associated adverse events.     

The role of aromatase inhibitors in early breast cancer

Opinion statement The role of hormonal therapy for the treatment of patients with early stage breast cancer has been evaluated in many studies. The results of these studies establish tamoxifen as the gold standard of hormonal therapy for the adjuvant treatment of hormone receptorpositive invasive breast cancer in pre- and postmenopausal women. Studies show tamoxifen reduces the risk of invasive breast cancer in women at increased risk for the disease, including women with ductal carcinoma in situ. Tamoxifen has adverse effects such as hot flashes, increased risk of uterine cancer in postmenopausal women, and rare occurrence of thromboembolic disease. Despite the multiple therapeutic roles of tamoxifen, alternatives are needed. Aromatase inhibitors (AI) are drugs with antiestrogenic activity. AIs function by inhibiting the peripheral conversion of adrenally synthesized androstenedione to estradiol through inhibition of the aromatase enzyme. AIs do not suppress estradiol synthesis by the ovary adequately. Therefore, AIs are effective in reducing circulating estradiol levels in postmenopausal women, but not premenopausal women. Selective nonsteroidal AIs, including anastrozole (Arimidex; AstraZeneca, Wilmington, DE) and letrozole (Femara; Novartis, East Hanover, NJ), and the steroidal AI exemestane (Aromasin; Pharmacia, Peapack, NJ) have been associated with increased specificity and improved therapeutic index compared to nonselective AIs such as aminoglutethamide. Nonsteroidal and steroidal AIs have demonstrated to be superior to megestrol acetate in second-line therapy of postmenopausal women with metastatic breast cancer, and selective nonsteroidal AIs have shown to be superior to tamoxifen in first-line therapy of postmenopausal women with metastatic breast cancer. The ATAC (Arimidex, tamoxifen, alone, or in combination) trial is the only published randomized trial comparing the efficacy of an AI to tamoxifen for the adjuvant treatment of women with early breast cancer. This large study showed that at a median follow-up time of 33 months, anastrozole alone results in significant improvement in disease-free survival rates, reduction in contralateral breast cancers, and increased tolerability, compared to tamoxifen in postmenopausal women. Although the long-term effects of AIs are not known, the early positive results of the ATAC trial led to the approval of anastrozole by the US Food and Drug Administration for use as adjuvant hormonal therapy for postmenopausal women with hormone receptor-positive invasive breast cancer. Thus, there is an alternative to tamoxifen for postmenopausal women with relative/absolute contraindications to tamoxifen use or patients who choose not to take tamoxifen because of its side-effect profile. New AIs may challenge the position of tamoxifen as the gold standard for the treatment of early stage breast cancer in postmenopausal women.     

Aromatase inhibitors for the treatment and prevention of breast cancer

In a review of current information on aromatase inhibitors (AIs) and their use in breast cancer treatment and prevention, published reports were obtained through a Medline search. Tamoxifen, a selective estrogen receptor modulator, is approved for use in metastatic breast cancer (MBC), the adjuvant treatment of breast cancer, and the prevention of breast cancer in women at high risk. The 50% reduction in breast cancer incidence seen with tamoxifen is significant for women at increased risk but is accompanied by notable toxicities such as thrombotic events and endometrial cancer. Therefore, the development of other effective agents with less toxicity would be a major advance in breast cancer prevention. Aromatase inhibitors, recently approved for the treatment of MBC and in the adjuvant setting, are proving to be slightly more effective than tamoxifen therapy. These drugs, approved for use in only postmenopausal women, inhibit the enzyme aromatase and thereby lower circulating functional estrogen. To date, the most concerning side effect of these agents is an increase in fracture rate. Compared with tamoxifen, thrombotic events and endometrial cancer rates are much lower. Ongoing data from the Arimidex, Tamoxifen, Alone or in Combination trial continue to favor anastrozole over tamoxifen in the reduction of primary contralateral breast cancers. This information has prompted breast cancer chemoprevention trials with AIs. Although tamoxifen is the gold standard for prevention therapy, results of ongoing studies may indicate a role for AIs in the prevention of breast cancer.     

Adjuvant aromatase inhibitors following tamoxifen for early-stage breast cancer in postmenopausal women: what do we really know?

Adjuvant hormonal therapy in the treatment of women with early-stage, hormone receptor (HR)-positive breast cancer is now considered the standard of care. Adjuvant tamoxifen decreases the risk of breast cancer recurrence and death in women with early-stage breast cancer when taken for 5 years. The benefits of tamoxifen are counterbalanced by toxicities including an increased risk of endometrial cancer and thromboembolic events. The selective aromatase inhibitors (AIs)--including anastrozole, letrozole, and exemestane--are challenging the role of tamoxifen as the adjuvant hormonal therapy of choice in postmenopausal women. Results of the Arimidex and Tamoxifen Alone or in Combination trial favor the use of anastrozole over tamoxifen as initial adjuvant hormonal therapy, with improvement in disease-free survival (DFS) and a favorable toxicity profile. The results of 2 large adjuvant trials using AIs sequentially with tamoxifen in postmenopausal women with early-stage, HR-positive breast cancer have been reported. The MA-17 study randomized women to placebo or letrozole for 5 years after completion of 4.5-6 years of initial tamoxifen. The Intergroup Exemestane Study (IES) randomized women following 2-3 years of adjuvant tamoxifen to continue to receive tamoxifen or switch to exemestane for a total of 5 years of adjuvant hormonal therapy. The MA-17 and IES trials demonstrated superior DFS with the AI and corroborated the smaller GROCTA-4B and Italian Tamoxifen Arimidex trials, which studied sequential therapy with aminoglutethamide or anastrozole. There is now substantial medical evidence supporting the use of AIs in postmenopausal women with early-stage, HR-positive breast cancer.     

Skeletal health in postmenopausal survivors of early breast cancer

Estrogen plays an important role in the skeletal health of all women. Many therapies used in the treatment of breast cancer reduce estrogen levels and have the potential to affect bone negatively by increasing the risk of osteoporosis and associated bone fractures. The long-term effects of systemic endocrine therapy on bone, therefore, are an important consideration in the adjuvant setting. Tamoxifen has been shown to have a moderate protective effect on postmenopausal bone due to its partial estrogen agonist activity; however, its long-term use is potentially associated with negative side effects, such as an increased risk of thromboembolic disease and endometrial cancer. Newer agents, the third-generation aromatase inhibitors (AIs), anastrozole, letrozole and exemestane, for example, do not possess estrogen agonist effects and have improved breast cancer outcomes when compared to the standard 5 years of tamoxifen. However, patients treated with adjuvant AIs have been shown to have an increased incidence of osteoporosis and osteoporotic fractures. In order to select the optimal adjuvant therapy for each patient, it is important to assess the overall risk:benefit ratio for each endocrine strategy. All postmenopausal women should follow published guidelines to assess the risk of osteoporosis and, where appropriate, they should receive bone mineral density monitoring. Postmenopausal women with breast cancer who are at increased risk of osteoporotic fracture should be identified and managed with appropriate nonpharmacologic and pharmacologic measures.     

Aromatase inhibitor therapy: toxicities and management strategies in the treatment of postmenopausal women with hormone-sensitive early breast cancer

Aromatase inhibitors (AIs) have been shown to reduce the risk of breast cancer recurrence and are widely used today as adjuvant therapy in women with early stage endocrine-responsive breast cancer. Aromatase inhibitors may be prescribed as initial hormonal therapy, sequentially following 2–3 years of tamoxifen, or as extended adjuvant therapy (following 5 years of tamoxifen). Aromatase inhibitors are generally well tolerated; however, certain side effects, particularly arthralgia/musculoskeletal symptoms and gynecologic effects, may result in poor adherence to treatment. Patients receiving adjuvant therapy with an AI should be counseled regarding possible side effects and the importance of completing treatment. Interventions to ameliorate side effects should be individualized based on symptoms, comorbid conditions, and pre-existing therapies. In addition, bone and cardiovascular health should be monitored during AI therapy. Prompt therapeutic management of common side effects associated with AIs may provide patients with the opportunity to receive the full benefit of their adjuvant hormonal treatment while minimizing toxicity.     

A woman's heart

Adjuvant therapy in postmenopausal women with breast cancer may contribute to the expression of underlying cardiovascular disease or expose the heart to additional toxicities. Tamoxifen remains an important component of endocrine therapy for breast cancer, although major clinical trials of the aromatase inhibitors (AIs) anastrozole, letrozole, and exemestane suggest that these agents are more effective and better tolerated alternatives to tamoxifen. The AIs inhibit the conversion of androgens to estrogen in postmenopausal women; consequently, their mechanism of action differs from that of tamoxifen. Accordingly, although it has been observed that tamoxifen has some favorable effects on cardiovascular risk, such as reducing total cholesterol levels, because of its partial estrogen‐agonist properties, no such effects exist for the AIs. Some studies, particularly those that compare the AIs with tamoxifen, have suggested a less favorable impact of adjuvant AI therapy on cardiovascular risk. Comorbid conditions, including cardiovascular disease, emerge as competing causes of death as women with breast cancer continue to live longer, and the potential impact of adjuvant therapies on cardiovascular risk becomes an increasingly important consideration for clinicians. Cancer 2009. © 2009 American Cancer Society.     

The breast cancer continuum in hormone-receptor-positive breast cancer in postmenopausal women: evolving management options focusing on aromatase inhibitors.

There are now a number of highly effective options for the treatment of hormone-receptor-positive breast cancer. Although tamoxifen was the standard hormonal treatment for many years, we now have another option for postmenopausal women: the third-generation aromatase inhibitors (AIs) anastrozole, exemestane and letrozole. A number of trials have investigated the use of third-generation AIs compared with tamoxifen throughout the continuum of treatment settings for postmenopausal women with breast cancer. In the neoadjuvant setting, letrozole, given for 4 months, resulted in better overall clinical response and breast-conserving surgery rates than tamoxifen. The Immediate Preoperative Anastrozole Tamoxifen or Combined with Tamoxifen trial gave anastrozole for 3 months with no difference in clinical response but significantly improved breast-conserving surgery rates. Compared with tamoxifen, anastrozole and letrozole significantly improved disease-free survival as early adjuvant treatment for hormone-receptor-positive disease. Switching to anastrozole or exemestane after 2 to 3 years of adjuvant tamoxifen for a total of 5 years of therapy was also more effective than continued tamoxifen. All three agents are approved in the early adjuvant or switching setting in the USA. Letrozole following 5 years of tamoxifen as extended adjuvant treatment improved disease-free survival and, in the node-positive subgroup, overall survival when compared with placebo. Anastrozole and letrozole are both approved for the first-line treatment of hormone-sensitive advanced breast cancer in postmenopausal women; letrozole showed an improved response rate compared with tamoxifen. Anastrozole, letrozole and exemestane are all indicated for the second-line treatment of advanced breast cancer. In summary, third-generation AIs have been shown to have superior efficacy over tamoxifen in the metastatic, neoadjuvant and adjuvant settings and to improve outcome as extended adjuvant therapy following 5 years of tamoxifen. Ongoing studies will further define the role of sequential adjuvant treatment. Appropriate duration of treatment is another important area of investigation. This review will cover hormonal therapy for postmenopausal women with breast cancer and will not address the treatment of premenopausal women.     

Adjuvant endocrine therapy in postmenopausal women with early breast cancer: Where are we now?

Tamoxifen has been the standard of care for adjuvant endocrine therapy of early breast cancer. In postmenopausal women, data now suggest that alternative agents (aromatase inhibitors [AIs]) may have improved long-term risk:benefit profiles and thus have the potential to improve outcome. The 'Arimidex', Tamoxifen, alone or in combination (ATAC) trial has shown that anastrozole provides improved disease-free survival (DFS) and time to recurrence, significantly reduced time to distant metastases and superior overall tolerability compared with tamoxifen when used as initial adjuvant therapy. Results have already led to a reconsideration of current recommendations for adjuvant therapy. Other ongoing trials include studies that are evaluating the benefits of sequencing of endocrine agents both within the standard 5-year adjuvant treatment period and as additional therapy in the post-adjuvant period. Three recently reported trials have suggested that switching from tamoxifen to an AI after 2-3 years of treatment leads to better outcomes than 5 years of tamoxifen. Finally, the NCIC MA 17 trial has shown that switching to an AI after 5 years of tamoxifen improves DFS compared with placebo. These are momentous discoveries that have improved our biological understanding and will inevitably change the management of breast cancer in the near future.     

Safety of aromatase inhibitors in the adjuvant setting

The third-generation aromatase inhibitors (AIs) letrozole, anastrozole, and exemestane are replacing tamoxifen as adjuvant therapy in most postmenopausal women with early breast cancer. Although AIs have demonstrated superior efficacy and better overall safety compared with tamoxifen in randomized controlled trials, they may not provide the cardioprotective effects of tamoxifen, and bone loss may be a concern with their long-term adjuvant use. Patients require regular bone mineral density monitoring, and prophylactic bisphosphonates are being evaluated to determine whether they may protect long-term bone health. AIs decrease the risks of thromboembolic and cerebrovascular events compared with tamoxifen, and the overall rate of cardiovascular events in patients treated with AIs is within the range seen in age-matched, non-breast-cancer populations. AIs are also associated with a lower incidence of endometrial cancer and fewer vaginal bleeding/discharge events than tamoxifen. Compared with tamoxifen, the incidence of hot flashes is lower with anastrozole and letrozole but may be higher with exemestane. Generally, adverse events with AIs are predictable and manageable, whereas tamoxifen may be associated with life-threatening events in a minority of patients. Overall, the benefits of AIs over tamoxifen are achieved without compromising overall quality of life.     

Current topics and perspectives on the use of aromatase inhibitors in the treatment of breast cancer

Tamoxifen has played a central role in endocrine therapy for hormone-responsive breast cancer. Results of recent clinical trials have, however, clearly shown that third-generation aromatase inhibitors (AIs), such as anastrozole, letrozole and exemestane, are superior to tamoxifen in the treatment of postmenopausal patients with metastatic breast cancer, in an adjuvant setting and for early breast cancer. Many studies have been published that describe new results from clinical trials and how they fundamentally prove the efficacy of AIs. There are, however, still some unresolved issues concerning the applications of AIs, such as the optimal duration of the therapy, the optimal regimens (initial, adjuvant or switching from tamoxifen to AI), and combination with LH–RH agonists for premenopausal woman. These issues are discussed in this review. Additionally, further possibilities for the application of AIs, for example in combination therapy with pure antiestrogen aimed at complete estrogen blockade and in combination with new biological agents, as well as the pharmacogenomics of AIs will be discussed.     

Aromatase inhibitors for breast cancer: proven efficacy across the spectrum of disease

For more than 100 years, hormonal therapy has been known to be effective in the treatment of breast cancer. Initially, this therapy was dominated by the selective estrogen receptor antagonists such as tamoxifen. Aromatase inhibitors (AIs) are a distinct drug class with demonstrated activity in the treatment of hormone-sensitive breast cancer. All 3 third-generation AIs, exemestane, anastrozole, and letrozole, have been studied in multiple lines of therapy in advanced breast cancer and have demonstrated equivalence or superiority compared with tamoxifen. While initially developed as a treatment option for advanced disease, the AIs have also shown efficacy in the treatment of curable disease, including the neoadjuvant and adjuvant settings. In addition, the AIs demonstrate a tolerable side effect profile in comparison with tamoxifen, and this has led to their early incorporation as standard of care therapy. Given the proven efficacy of AIs across the spectrum of breast cancer, the remaining questions include definitive sequencing strategy, timing, and duration of use. Ongoing trials include head-to-head comparisons between the AIs in early-stage breast cancer; the results of these trials are eagerly anticipated and should further optimize the use of AIs.     

The role of tamoxifen in the treatment and prevention of breast cancer.

Tamoxifen is a nonsteroidal antiestrogen that has found successful applications for each stage of breast cancer in the treatment of selected patients. Tamoxifen was originally introduced for the treatment of advanced disease in postmenopausal women; however, the drug is now also available for the palliative treatment of premenopausal women with estrogen receptor (ER) positive disease. The proven efficacy of tamoxifen and the low incidence of side effects made the drug an ideal agent to test as an adjuvant therapy for women with node-positive breast cancer. Laboratory studies indicate that long-term treatment schedules may provide maximal benefit in preventing recurrence, and recent analysis of clinical trials demonstrates that between 2 and 5 years of adjuvant tamoxifen therapy provides a survival advantage for postmenopausal women with node-positive disease. Similarly, adjuvant studies in node-negative breast cancer have demonstrated an increase in the disease-free survival of both pre- and postmenopausal patients with ER-positive tumors. However, the extended use of tamoxifen has raised questions about the long-term safety of antiestrogen therapy. Of special concern is the impact of tamoxifen on ovarian function in premenopausal women and the potential risks to the fetus if pregnancy occurs. Fortunately, there are no reports about the teratogenicity of tamoxifen in the human, but it is important that physicians counsel women about the risk of pregnancy. Tamoxifen should not be used if a patient is pregnant. Initial concerns that the long-term administration of an antiestrogen would increase bone loss and increase the risks of coronary heart disease appear to be unwarranted. Tamoxifen has some estrogen-like activities in postmenopausal women and causes a preservation of bone in the lumbar spine and a decrease in circulating cholesterol. Indeed, a reduction in fatal myocardial infarction (MI) has been noted during 5 years of tamoxifen therapy, possibly the direct result of a prolonged reduction in circulating cholesterol. However, the estrogen-like qualities of tamoxifen that could be valuable as a hormone replacement therapy for all postmenopausal women following a diagnosis of breast cancer may also increase the risk for developing endometrial carcinoma. To date, there are only a few reports of endometrial carcinoma being diagnosed during adjuvant therapy with tamoxifen; however, any instances of uterine bleeding or spotting should be followed up with an endometrial biopsy. There are some concerns about large doses of tamoxifen promoting liver cancer in rats. These results are of particular concern if tamoxifen is to be used as a preventive in normal women.(ABSTRACT TRUNCATED AT 400 WORDS)     

Reducing the risk of distant metastases in breast cancer patients: role of aromatase inhibitors

Breast cancer continues to be one of the most prominent causes of cancer death among women worldwide. Mortality in breast cancer is most commonly caused by the occurrence of distant metastases. Thus, treatments that reduce the risk of distant metastases are likely to improve survival. The third-generation aromatase inhibitors (AIs), including anastrozole, letrozole, and exemestane, have been investigated as alternatives to tamoxifen for the adjuvant treatment of early, endocrine-responsive breast cancer. Results from several large trials have established the superior efficacy of the AIs over tamoxifen in reducing the risk of recurrences when used as upfront, switch, and extended adjuvant therapy. Here, we review recent updated results obtained with AIs as adjuvant therapy, in terms of reducing the risk of distant metastases.     

The use of aromatase inhibitors in adjuvant therapy for early breast cancer

Clinical evidence supporting the use of aromatase inhibitors (AIs) in adjuvant therapy for hormone-sensitive early breast cancer (EBC) has grown rapidly over the past few years and is reviewed in this article. The results of two studies-the Arimidex, Tamoxifen, Alone or in Combination (ATAC) trial and the Breast International Group (BIG) 1-98 trial-support the use of AIs as primary adjuvant therapy for EBC, with significantly prolonged disease-free survival, time to recurrence, and time to distant recurrence for both anastrozole and letrozole over tamoxifen. Furthermore, anastrozole has an established beneficial risk:benefit ratio compared with tamoxifen with mature data over the full 5-year recommended treatment period. For women who have already received 2-3 years of tamoxifen, switching studies with anastrozole [the Italian Tamoxifen Anastrozole (ITA) trial and the Austrian Breast and Colorectal Cancer Study Group (ABCSG) 8/Arimidex-Nolvadex (ARNO 95) trial] and exemestane [the Intergroup Exemestane Study (IES)] have also shown that 5 years of primary adjuvant tamoxifen therapy is not optimal and that switching to an AI should be considered. Finally, for those women who have completed 5 years of tamoxifen, based on the results of the MA 17 trial, extended adjuvant treatment with letrozole should be considered. Although no sequencing data are available yet, current evidence suggests that an AI should be the adjuvant treatment of choice over tamoxifen, and anastrozole is the only AI with mature adjuvant data to date.     

Advances in endocrine treatments for postmenopausal women with metastatic and early breast cancer

For the past 25 years, the estrogen antagonist tamoxifen has been the hormonal treatment of choice for postmenopausal patients with hormone-sensitive metastatic and early breast cancer (EBC). However, tamoxifen is associated with certain tolerability and safety concerns. In addition, the hormonal options after progression are limited, and thus, alternative endocrine treatments have been developed. This review provides a synopsis of the newer alternatives in endocrine therapy of breast cancer: the aromatase inhibitors (AIs) and fulvestrant Faslodex), the estrogen receptor antagonist that downregulates estrogen and progesterone receptors and has no known agonist activity. The third-generation AIs, anastrozole and letrozole, have been shown to be as effective or more effective than megestrol acetate and tamoxifen as second- and first-line therapies for the treatment of postmenopausal patients with metastatic breast cancer, and exemestane has been approved for second-line use. Fulvestrant has been shown to be as effective as anastrozole as second-line therapy for metastatic breast cancer and has been approved in the U.S. for the treatment of postmenopausal women with hormone-receptor-positive metastatic breast cancer following progression on antiestrogen therapy. Anastrozole is the only AI with published clinical trial data and U.S. Food and Drug Administration approval for adjuvant therapy of postmenopausal women with EBC. The 'Arimidex,' Tamoxifen, Alone or in Combination (ATAC) trial, a double-blind, multicenter trial with 9,366 patients, compared tamoxifen with anastrozole, alone and in combination, as adjuvant endocrine treatment for postmenopausal patients with operable, invasive, EBC. The first analysis (at a median follow-up of 33.3 months) showed longer disease-free survival and, in general, better tolerability with anastrozole than with tamoxifen. This pattern was maintained at later analyses with a median follow-up of 47 months for efficacy and 37 months for safety and tolerability. Although longer follow-up is warranted, anastrozole appears to be a well-documented choice of endocrine adjuvant therapy for postmenopausal women with hormone-responsive breast cancer.