Chemoprevention Strategies 2006

Opinion statement Several large, prospective trials have evaluated tamoxifen compared with placebo for breast cancer risk reduction in women at increased risk for breast cancer. The risk of developing breast cancer is the primary determinant of net benefit, with greater net benefits accruing to women with the highest risk of breast cancer. Both age and the presence of factors that increase the risk of toxicity have the greatest effect on the net benefit associated with tamoxifen. The greatest clinical benefit with least side effects is derived from the use of tamoxifen in younger, premenopausal women who are less likely to have thromboembolic complications and uterine cancer, in women without a uterus, and in women at higher breast cancer risk such as those with atypical hyperplasia or lobular carcinoma in situ. Tamoxifen may offer benefit to women who are carriers of BRCA2 mutations, although no prospective trials have been conducted. Compared to placebo in postmenopausal women at average risk of breast cancer in published trials of osteoporosis, raloxifene reduces the risk of invasive breast cancer. Among younger postmenopausal women who are at increased risk of breast cancer, raloxifene is as effective as tamoxifen in reducing the risk of invasive breast cancer. Raloxifene appears to be less effective than tamoxifen in reducing the risk of in situ breast cancer. In high-risk, younger, postmenopausal women, raloxifene appears to offer net benefit when comparing reduction of the risk of breast cancer and the prevention of fractures with the risk of stroke, venous thromboembolic events, uterine events, as well as symptomatic side effects.     

Update on breast cancer prevention

Four randomized prospective trials have evaluated tamoxifen for chemoprevention of breast cancer. The National Surgical Adjuvant Breast and Bowel Project P-1 trial reported that tamoxifen reduced the risk of invasive breast cancer by 49%. Two smaller European trials, the Royal Marsden Hospital Chemoprevention Trial and the Italian Tamoxifen Prevention Study, demonstrated no decrease in the incidence of breast cancer among women using tamoxifen. The International Breast Cancer Intervention Study confirmed that tamoxifen can reduce the risk of breast cancer in healthy women. The Multiple Outcomes of Raloxifene Evaluation trial, which evaluated the use of raloxifene (Evista) to prevent osteoporosis, found that the risk of invasive breast cancer decreased by 76%. A uniform theme in these trials is that tamoxifen reduces the risk of breast cancer among women at high risk for the disease. Tamoxifen is currently approved for breast cancer risk reduction. However, because of the side effects associated with its use (i.e., endometrial cancer and thromboembolism), other agents are being investigated. The Study of Tamoxifen and Raloxifene is designed to compare the efficacy of tamoxifen and raloxifene in reducing breast cancer risk. Aromatase inhibitors will also be studied in the setting of chemoprevention for breast cancer.     

Selective estrogen-receptor modulators in 2001

Tamoxifen (Nolvadex), a selective estrogen-receptor modulator, or SERM, is currently the endocrine therapy of choice for all stages of hormone-responsive breast cancer. Only tamoxifen has been approved by the US Food and Drug Administration to reduce the incidence of breast cancer in high-risk women. Despite tamoxifen's antiestrogenic effects in breast tissue, it exhibits paradoxical estrogenic effects in other tissues in the body. These effects result in the maintenance of bone mineral density, but a three- to fourfold increase in endometrial cancer in postmenopausal women. Additionally, tamoxifen can result in troublesome hot flashes and serious thromboembolic events. For this reason, current research is focusing on new agents that may maintain the beneficial effects of tamoxifen while reducing its adverse effects. Raloxifene (Evista) is another SERM, approved for the prevention of osteoporosis in postmenopausal women and now being compared with tamoxifen in an ongoing breast cancer prevention trial. Like tamoxifen, raloxifene is associated with hot flashes and thromboembolic events, but its association with the risk of endometrial cancer is unknown. A number of new SERMs are in preclinical or clinical development in an attempt to improve upon the safety profile of tamoxifen. Additionally, selective aromatase inhibitors are being examined in the early breast cancer setting.     

The role of selective estrogen receptor modulators in the prevention of breast cancer: comparison of the clinical trials

The role of estrogen in the development of breast cancer is well recognized, and the use of selective estrogen receptor modulators (SERMs) to reduce breast cancer risk continues to be evaluated. Tamoxifen is the only SERM approved for the reduction of breast cancer incidence in women at high risk. This approval was based on results from the Breast Cancer Prevention Trial. Although initial results from the Royal Marsden Hospital tamoxifen trial and Italian Tamoxifen Prevention Study did not show a similar overall effect of tamoxifen, recent updates from these two trials and initial results from the International Breast Cancer Intervention Study are consistent with a risk reduction effect of tamoxifen for estrogen-receptor-positive breast cancer. Raloxifene, approved for the prevention and treatment of postmenopausal osteoporosis, is another SERM being evaluated for breast cancer risk reduction. The recently completed Continuing Outcomes Relevant to Evista trial and the Raloxifene Use for The Heart trial, have breast cancer risk reduction as a primary end point. A third, ongoing trial, the Study of Tamoxifen and Raloxifene trial, is evaluating the relative efficacy and adverse event profile of these two agents in a population at high risk. The study populations of these raloxifene breast cancer prevention trials and the four tamoxifen prevention trials are quite diverse in terms of breast cancer risk. Completion of these trials will provide important information about the occurrence of invasive breast cancer in postmenopausal women and the efficacy of raloxifene for breast cancer risk reduction.     

Haemostatic changes and thromboembolic risk during tamoxifen therapy in normal women.

Tamoxifen has been implicated as a risk factor for venous thrombosis in advanced breast cancer although the evidence for increased arterial or venous thrombosis with tamoxifen in early breast cancer is less clear. The effect of tamoxifen on haemostasis, and thereby possible thromboembolic risk, was investigated in normal women enrolled in a placebo controlled trial of tamoxifen as a chemopreventative agent for breast cancer. There was an initial reduction in fibrinogen levels in all women on tamoxifen over the first year of follow-up and a marginal reduction in antithrombin III and Protein S in postmenopausal women at 6 months. There were no changes in cross linked fibrinogen degradation products or Protein C for pre or post-menopausal women. There was no increase in the incidence of thromboembolic events on tamoxifen. This study demonstrates that tamoxifen has only marginal effects on factors involved in haemostasis reported to affect the incidence of arterial or venous thromboembolic disease. The follow-up time is relatively short (maximum 36 months) and careful long term follow-up is necessary to detect clinically significant morbidity.     

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.     

American Society of Clinical Oncology technology assessment on breast cancer risk reduction strategies: tamoxifen and raloxifene.

OBJECTIVE: To conduct an evidence-based technology assessment to determine whether tamoxifen and raloxifene as breast cancer risk-reduction strategies are appropriate for broad-based conventional use in clinical practice. POTENTIAL INTERVENTION: Tamoxifen and raloxifene. OUTCOME: Outcomes of interest include breast cancer incidence, breast cancer-specific survival, overall survival, and net health benefits. EVIDENCE: A comprehensive, formal literature review was conducted for tamoxifen and raloxifene on the following topics: breast cancer risk reduction; tamoxifen side effects and toxicity, including endometrial cancer risk; tamoxifen influences on nonmalignant diseases, including coronary heart disease and osteoporosis; and decision making by women at risk for breast cancer. Testimony was collected from invited experts and interested parties. VALUES: More weight was given to publications that described randomized trials. BENEFITS/HARMS/COSTS: The American Society of Clinical Oncology (ASCO) Working Group acknowledges that a woman's decision regarding breast cancer risk-reduction strategies will depend on the importance and weight attributed to the information provided regarding both cancer and non-cancer-related risks. CONCLUSIONS: For women with a defined 5-year projected risk of breast cancer of >/= 1.66%, tamoxifen (at 20 mg/d for up to 5 years) may be offered to reduce their risk. It is premature to recommend raloxifene use to lower the risk of developing breast cancer outside of a clinical trial setting. On the basis of available information, use of raloxifene should currently be reserved for its approved indication to prevent bone loss in postmenopausal women. Conclusions are based on single-agent use of the drugs. At the present time, the effect of using tamoxifen or raloxifene with other medications (such as hormone replacement therapy), or using tamoxifen and raloxifene in combination or sequentially, has not been studied adequately. The continuing use of placebo-controlled trials in other risk-reduction trials highlights the current unanswered issues concerning the use of such interventions, especially when the influence on net health benefit remains to be determined. Breast cancer risk reduction is a rapidly evolving area. This technology assessment represents an ongoing process with existing plans to monitor and review data and to update recommendations in a timely matter. (See VALIDATION: The conclusions of the Working Group were evaluated by the ASCO Health Services Research Committee and by the ASCO Board of Directors. SPONSOR: American Society of Clinical Oncology.     

The STAR trial: evidence for raloxifene as a breast cancer risk reduction agent for postmenopausal women

The 1998 approval of tamoxifen for breast cancer risk reduction opened the era of breast cancer chemoprevention. Women at increased risk for breast cancer now had an option other than healthy lifestyle and prophylactic surgery to reduce risk. However, women and their physicians were reluctant to use tamoxifen because of associated risks. Several trials investigating raloxifene suggested it may reduce breast cancer risk without having an apparent effect on the endometrium. The Study of Tamoxifen and Raloxifene (STAR) for the Prevention of Breast Cancer trial opened in 1999 to directly compare raloxifene to tamoxifen for breast cancer risk reduction. Since the unblinding of the STAR trial in 2006, raloxifene has emerged as an option for reducing breast cancer risk for postmenopausal women at increased risk for the disease.     

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.     

Hormonal interventions to prevent hormonal cancers: breast and prostate cancers.

In 1998, the concept of breast cancer prevention became a reality with the approval of tamoxifen to reduce the risk of developing breast cancer in women at increased risk for the disease. This approval was based on decades of research on selective estrogen receptor modulators providing an understanding of the role of the estrogen receptor in breast cell growth, and an appreciation of the carcinogenic process. Although results from the Breast Cancer Prevention Trial demonstrated a 49% reduction in breast cancer in women at increased risk, there were associated toxicities related to the estrogenic effects of tamoxifen; that is, deep vein thrombosis, pulmonary embolism, and endometrial cancer. In an effort to improve its benefit-risk profile, tamoxifen is now being compared with raloxifene, a selective estrogen receptor modulator approved for the treatment and prevention of osteoporosis. This equivalency prevention Study of Tamoxifen and Raloxifene completed accrual of 19 747 high-risk postmenopausal women in November 2004. Meanwhile, another class of estrogen-directed drugs, the aromatase inhibitors, have shown efficacy in breast cancer adjuvant trials, spawning a number of prevention trials that have recently been initiated. As with breast cancer the hormonal contribution to prostate carcinogenesis was the basis for the Prostate Cancer Prevention Trial which showed that finasteride, an androgen antagonist, reduces the incidence of prostate cancer compared to placebo.     

Breast cancer risk management

Breast cancer is a devastating illness that affects tens of thousands of American women each year. Although no one can predict who will actually develop breast cancer, a number of risk factors have been found that allow clinicians to identify the women at highest risk. Recent research has focused on exploring options, such as chemoprevention, to prevent high-risk women from developing breast cancer. The selective estrogen receptor (ER) modulators (SERMs) were a logical choice for chemoprevention because of their well-known estrogen antagonist effects in the breast. Tamoxifen is the best studied of these agents and has been shown to reduce the incidence of all breast cancers by 38% and ER-positive tumors by 48%.(1) However, despite this large potential risk reduction, risk management with chemopreventive agents is still not routine. The primary deterrents are believed to be the significant adverse events associated with tamoxifen as well as a perceived decline in quality of life (QOL).(2-4) These concerns led researchers to consider other possible agents that would still be effective but would have fewer or more acceptable side effects than tamoxifen. Raloxifene was proposed as an alternative to tamoxifen based on its estrogen antagonist effects in the breast and its relative safety as an osteoporosis agent. In this article, we will review the trials that led to the emergence of both tamoxifen and raloxifene as chemopreventive agents and will then offer a management strategy for breast cancer prevention in the primary care setting.     

Tamoxifen and aromatase inhibitors in the treatment of breast cancer in menopausal women: pharmacological and clinical aspects

Estrogen is the main hormone involved in the development and growth of hormone-dependent breast cancer. Endocrine adjuvant treatment in recent years focused primarily on the use of SERMs, mainly tamoxifen. Tamoxifen actions are complex. It acts by competitive antagonism of estrogen at its receptor site. It has beneficial agonistic effects in preventing bone demineralization in postmenopausal women, but a detrimental agonistic effect by increasing the risk of uterine cancer and of thrombo-embolism. However, the situation is changing rapidly with the introduction of recent aromatase inhibitors, which display high specificity towards aromatase. They suppress plasma estrogen levels in postmenopausal women by inhibiting or inactivating aromatase, the enzyme responsible of the synthesis of estrogens from androgenic substrates. A complete estrogen deprivation in target tissues may eventually induce osteoporosis. Unlike tamoxifen, aromatase inhibitors have no partial agonistic action. During the last 20 years, adjuvant tamoxifen treatment for 5 years was the "gold standard" endocrine treatment in postmenopausal women with hormone-receptor-positive breast cancers. A 25% reduction risk of deaths was observed. Recently, the results of clinical trials comparing aromatase inhibitors to tamoxifen in post menopausal women with hormone-dependent breast cancer showed a benefit in favor of aromatase inhibitors in reducing the risk of recurrence. These trials were either comparative (for anastrozole) or sequential (for anastrozole, letrozole and exemestane). The issues of long term adverse effects (bone) and hormone treatment sequence remain to be addressed.     

Breast cancer adjuvant endocrine therapy

Adjuvant endocrine therapy with the selective estrogen receptor modulator, tamoxifen, has significantly improved mortality from early-stage breast cancer for both pre- and postmenopausal women with hormone receptor-positive breast cancer. Recent large clinical trials have demonstrated a clear and consistent benefit for the incorporation of aromatase inhibitor (AI) therapy within adjuvant endocrine regimens for postmenopausal women. The AIs, which are associated with myalgias, arthralgias, and a reduction in bone mineral density, are generally well tolerated and have lower risks of endometrial carcinoma and thromboembolic events than tamoxifen. Data are awaited from ongoing trials to better define the optimal sequencing strategy, duration, and AI agent. Attempts to further optimize adjuvant endocrine therapy by identifying predictive biomarkers of response, as well as by developing strategies to overcome endocrine resistance are underway. In premenopausal women AI monotherapy is currently contraindicated and tamoxifen remains the standard of care. The role of ovarian function suppression in addition to tamoxifen or combined with AI therapy is being explored. The hope is that continued advances in endocrine therapy will translate into improved survival among both pre- and postmenopausal women with receptor-positive breast cancer.     

Tamoxifen in Axillary Node-Negative Breast Cancer: Multisystem Benefits and Risks

Adjuvant tamoxifen therapy is associated with modest improvement in disease-free and overall survival in women with invasive axillary node-negative breast cancer. The preponderance of data supporting these general conclusions are from trials in postmenopausal women; in premenopausal women data appear convincing regarding disease-free, hut not overall, survival. Firm conclusions regarding magnitude of benefit related to presence of different prognostic factors cannot be drawn at present.

In postmenopausal women tamoxifen appears to alter favorably some risk factors for cardiovascular diseases and osteoporosis, which are the most common causes of mortality or morbidity in older American women. Adjuvant tamoxifen is associated with a significantly reduced risk of second primary breast cancer. Major serious risks of tamoxifen therapy include depression, and possibly thrombophlebitis and uterine endometrial cancer. Symptomatic vasomotor and gynecological side effects are frequent. Decision making with women should include assessment of these multisystem benefits and risks.     

Body mass index and the risk for developing invasive breast cancer among high-risk women in NSABP P-1 and STAR breast cancer prevention trials

High body mass index (BMI) has been associated with an increased risk for breast cancer among postmenopausal women. However, the relationship between BMI and breast cancer risk in premenopausal women has remained unclear. Data from two large prevention trials conducted by the National Surgical Adjuvant Breast and Bowel Project (NSABP) were used to explore the relationship between baseline BMI and breast cancer risk. The analyses included 12,243 participants with 253 invasive breast cancer events from the Breast Cancer Prevention Trial (P-1) and 19,488 participants with 557 events from the Study of Tamoxifen and Raloxifene (STAR). Both studies enrolled high-risk women (Gail score ≥ 1.66) with no breast cancer history. Women in P-1 were pre- and postmenopausal, whereas women in STAR (P-2) were all postmenopausal at entry. Using Cox proportional hazards regression, we found slight but nonsignificant increased risks of invasive breast cancer among overweight and obese postmenopausal participants in STAR and P-1. Among premenopausal participants, an increased risk of invasive breast cancer was significantly associated with higher BMI (P = 0.01). Compared with BMI less than 25, adjusted HRs for premenopausal women were 1.59 for BMI 25 to 29.9 and 1.70 for BMI 30 or more. Our investigation among annually screened, high-risk participants in randomized, breast cancer chemoprevention trials showed that higher levels of BMI were significantly associated with increased breast cancer risk in premenopausal women older than 35 years, but not postmenopausal women.     

Breast cancer prevention trials

A new option for women at increased risk for breast cancer is chemoprevention—namely, an attempt to decrease breast cancer incidence by means of drug therapy. The efficacy of tamoxifen as a chemopreventive agent has been studied to date in three randomized, controlled trials, with varying results. Investigators with the National Surgical Adjuvant Breast and Bowel Project (NSABP) Breast Cancer Prevention Trial found that tamoxifen reduced the incidence of breast cancer by almost half, whereas British and Italian researchers found no significant benefit. This disparity is due, in part, to differences in the baseline breast cancer risk characteristics among the study populations, differing cohort sizes, variable use of hormone replacement therapy, and other factors. In this article, we review the eligibility criteria, treatment plans, and results from the three published randomized trials of tamoxifen versus placebo. We also review the data on raloxifene and breast cancer incidence. Chemoprevention with tamoxifen, in a non-study setting, is one option for women at increased risk for breast cancer. The ongoing Study of Tamoxifen and Raloxifene (STAR) is a randomized, doubleblinded trial comparing the effectiveness of raloxifene with that of tamoxifen in postmenopausal women at increased risk for developing breast cancer. Until the results of this trial are available, it is premature to use raloxifene for primary breast cancer prevention.     

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 tamoxifen in breast-cancer-treatment in postmenopausal women - occurrence of thromboembolic complications

Of 441 postmenopausal breast cancer patients who received adjuvant tamoxifen, 19 had thromboembolic accidents (4.3%). All were in remission when thrombosis occurred. One patient died of bilateral pulmonary embolism. In the other cases, thromboembolic disorders were found to be reversible after the withdrawal of tamoxifen and anticoagulant treatment. Some patients had a history of vascular disorders, and others required prolonged bed rest which may have contributed as an aggravating circumstance to thrombotic events. Our study suggests that thromboembolic risk factors as well as potential vascular disorders induced by aggravating conditions have to be carefully examined in postmenopausal patients treated by adjuvant tamoxifen therapy. This is especially true in women with lobular breast cancer and aged more than 60 years.     

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.     

Tamoxifen to raloxifene and beyond

Tamoxifen, a selective estrogen receptor modulator (SERM), is the treatment of choice for all stages of hormone-responsive breast cancer and has been shown to prevent breast cancer in high-risk women. Despite acting as an antiestrogen on the breast, tamoxifen has partial estrogenic effects on other target tissues. These partial estrogen agonistic actions produce beneficial effects on bones and the lipid profile in postmenopausal women. However, tamoxifen is associated with an increase in endometrial cancer. Additionally, its antiestrogenic effects in the central nervous system result in hot flashes in postmenopausal women. Raloxifene is another SERM approved for the prevention of osteoporosis in postmenopausal women. Like tamoxifen, raloxifene appears to prevent breast cancer in high-risk women and has not, to date, been noted to increase the incidence of endometrial cancer. The Study of Tamoxifen and Raloxifene will compare the effects of the two agents on breast cancer prevention and endometrial cancer risk. A number of new agents are being developed for breast cancer treatment and prevention and osteoporosis prevention. These include other SERMs, selective estrogen receptor downregulators (SERDs), and aromatase inhibitors. It is hoped that one of these new agents will be the ideal agent, acting as an antiestrogen on breast and endometrium while having estrogenic effects on bones, the lipid profile, and the central nervous system. Semin Oncol 28:260-273.