Myocardial infarction risk and tamoxifen therapy for breast cancer

The beneficial effects of tamoxifen on arteries: a key player for cardiovascular health of breast cancer patient

Breast cancer is the most common cancer in women. Over the past few decades, advances in cancer detection and treatment have significantly improved survival rate of breast cancer patients. However, due to the cardiovascular toxicity of cancer treatments (chemotherapy, anti-HER2 antibodies and radiotherapy), cardiovascular diseases (CVD) have become an increasingly important cause of long-term morbidity and mortality in breast cancer survivors. Endocrine therapies are prescribed to reduce the risk of recurrence and specific death in estrogen receptor-positive (ER+) early breast cancer patients, but their impact on CVD is a matter of debate. Whereas aromatase inhibitors and luteinizing hormone-releasing hormone (LHRH) analogs inhibit estrogen synthesis, tamoxifen acts as a selective estrogen receptor modulator (SERM), opposing estrogen action in the breast but mimicking their actions in other tissues, including arteries. This review aims to summarize the main clinical and experimental studies reporting the effects of tamoxifen on CVD. In addition, we will discuss how recent findings on the mechanisms of action of these therapies may contribute to a better understanding and anticipation of CVD risk in breast cancer patients.

Coronary Artery Disease in Young Women After Radiation Therapy for Breast Cancer: The WECARE Study

Background

Radiation therapy (RT) for breast cancer increases risk of coronary artery disease (CAD). Women treated for left- vs right-sided breast cancer receive greater heart radiation exposure, which may further increase this risk. The risk of radiation-associated CAD specifically among younger breast cancer survivors is not well defined.

Objectives

The purpose of this study was to report CAD risk among participants in the Women's Environmental Cancer and Radiation Epidemiology Study.

Methods

A total of 1,583 women who were <55 years of age when diagnosed with breast cancer between 1985 and 2008 completed a cardiovascular health questionnaire. Risk of radiation-associated CAD was evaluated by comparing women treated with left-sided RT with women treated with right-sided RT using multivariable Cox proportional hazards models. Effect modification by treatment and cardiovascular risk factors was examined.

Results

In total, 517 women who did not receive RT and 94 women who had a pre-existing cardiovascular disease diagnosis were excluded, leaving 972 women eligible for analysis. Their median follow-up time was 14 years (range 1-29 years). The 27.5-year cumulative incidences of CAD for women receiving left- vs right-sided RT were 10.5% and 5.8%, respectively (P = 0.010). The corresponding HR of CAD for left- vs right-sided RT in the multivariable Cox model was 2.5 (95% CI: 1.3-4.7). There was no statistically significant effect modification by any factor evaluated.

Conclusions

Young women treated with RT for left-sided breast cancer had over twice the risk of CAD compared with women treated with RT for right-sided breast cancer. Laterality of RT is independently associated with an increased risk of CAD and should be considered in survivorship care of younger breast cancer patients.

Cardiovascular events and mortality in a population-based cohort initially diagnosed with ductal carcinoma in situ

Background

Ductal carcinoma in situ (DCIS) patients are usually diagnosed through cancer screening programs, suggesting a healthy user effect. In this population-based cohort, we assessed the risk of cardiovascular events and mortality in DCIS patients.

Methods

Using the Korean National Health Insurance Service database, 13,740 women, who were initially diagnosed with DCIS between 2007 and 2013, were analyzed. A control group was matched according to age and the year of diagnosis at a 3:1 ratio (n = 41,220). Follow-up was performed until 2016. Subgroup analysis was performed according to the subsequent diagnosis of invasive breast cancer within 1 year: pure DCIS and DCIS+Invasive group.

Results

DCIS patients were more likely to have underlying diseases, higher incomes, and to live in urban districts compared to the control group. Women diagnosed of DCIS had lower myocardial infarct risk (hazard ratio [HR] 0.64; 95% confidence interval [CI] 0.46–0.90) and lower stroke risk (HR 0.77; 95% CI 0.60–0.98) compared to the control group. This trend of lower risk was sustained after adjusting for age, income, residence and comorbidities. The mortality rate was similar between the control group and pure DCIS patients but was higher in the DCIS+Invasive group (HR 1.63; 95% CI 1.34–1.98). However, after adjusting for age, income, residence and comorbidities, mortality did not differ between the control group and DCIS+Invasive group (HR 0.99; 95% CI 0.78–1.24).

Conclusions

DCIS patients were at lower risk for MI and stroke compared to a control group despite a higher rate of comorbidities, which may reflect changes in health behaviour. The importance of managing pre-existing comorbidities along with DCIS treatment should be emphasized.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-08494-0.

Endocrine therapy use and cardiovascular risk in postmenopausal breast cancer survivors

Objective

Examine the effect of tamoxifen and aromatase inhibitors (AIs) on the risk of 12 clinically relevant cardiovascular outcomes in postmenopausal female breast cancer survivors.

Methods

We carried out two prospective cohort studies among postmenopausal women with breast cancer in UK primary care and hospital data (2002–2016) and US Surveillance, Epidemiology and End Results-Medicare data (2008–2013). Using Cox adjusted proportional hazards models, we compared cardiovascular risks between AI and tamoxifen users; and in the USA, between users of both drug classes and women receiving no endocrine therapy.

Results

10 005 (UK) and 22 027 (USA) women with postmenopausal breast cancer were included. In both countries, there were higher coronary artery disease risks in AI compared with tamoxifen users (UK age-standardised incidence rate: 10.17 vs 7.51 per 1000 person-years, HR: 1.29, 95% CI 0.94 to 1.76; US age-standardised incidence rate: 36.82 vs 26.02 per 1000 person-years, HR: 1.29, 95% C I1.06 to 1.55). However, comparisons with those receiving no endocrine therapy (US data) showed no higher risk for either drug class and a lower risk in tamoxifen users (age-standardised incidence rate tamoxifen vs unexposed: 26.02 vs 35.19 per 1000 person-years, HR: 0.74, 95% 0.60 to 0.92; age-standardised incidence rate AI vs unexposed: 36.82 vs 35.19, HR: 0.96, 95% CI 0.83 to 1.10). Similar patterns were seen for other cardiovascular outcomes (arrhythmia, heart failure and valvular heart disease). As expected, there was more venous thromboembolism in tamoxifen compared with both AI users and those unexposed.

Conclusions

Higher risks of several cardiovascular outcomes among AI compared with tamoxifen users appeared to be driven by protective effects of tamoxifen, rather than cardiotoxic effects of AIs.

Effects of tamoxifen and aromatase inhibitors on the risk of acute coronary syndrome in elderly breast cancer patients: An analysis of nationwide data

Background

Aromatase inhibitors (AIs) are the preferred endocrine treatment for postmenopausal hormonal receptor-positive breast cancer. However, there is controversy on the long-term cardiovascular and cerebrovascular safety of AIs over that of tamoxifen.

Methods

We analyzed the National Health Information Database (NHID) of 281,255 women over a 20-year-old diagnosed with breast cancer between 2009 and 2016. Cardiovascular events (CVEs) were defined as the development of the following, acute coronary syndrome (ACS), ischemic and hemorrhagic stroke, defined by using insurance claim records. The model was constructed by Cox proportional hazard regression and this model was used to analyze the effects of AI and tamoxifen on CVE.

Results

We included 47,569 women for the final analysis. Patients were classified into ‘No hormonal treatment (n = 18,807), ‘Switch (n = 2097)’, ‘Tamoxifen (n = 7081)’ and ‘AI (n = 19,584)’. There were 2147 CVEs in 2032 patients (4.1%). Univariate analysis showed that women with tamoxifen had significantly lower risk for CVEs compared to no-treatment (hazard ratio (HR) 0.84, 95% confidence interval (CI) 0.74–0.97) while AI showed no such effect (HR 0.93, 95% CI 0.84–1.02). After adjusting for other risk factors (hypertension, dyslipidemia, family history), the use of tamoxifen was associated with significant protective effect against ACS (HR 0.63, 95% CI 0.47–0.84).

Conclusions

Our results, based on the NHID, supports the protective effect of tamoxifen against CVE in Korean breast cancer patients aged 55 and older that is not seen with AIs. Our results can guide the selection of adjuvant hormonal treatment agents for Korean breast cancer patients based on their risk of developing CVE.

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Controversy on the long-term cardiovascular and cerebrovascular safety of AIs over that of tamoxifen.

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The protective effect of tamoxifen against cardiovascular events in elderly breast cancer patients that is not seen with AIs.

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Choice of hormonal therapy depends on patient’s cardiovascular or cerebrovascular risks.

Risk Factors and Outcomes During a First Acute Myocardial Infarction in Breast Cancer Survivors Compared with Females Without Breast Cancer

PURPOSE

The purpose of this research was to study the differences in epidemiology and outcomes of a first myocardial infarction in breast cancer survivors compared with the general female population in the United States.

METHODS

We retrospectively analyzed the US National Inpatient Sample years 2005-2015 to identify adult women with a first myocardial infarction. In this cohort, breast cancer survivors were identified. Outcomes evaluated were the differences in baseline demographics, comorbidities, and adjusted in-hospital mortality in women with and without breast cancer.

RESULTS

Among 1,644,032 first myocardial infarction cases in adult women, there were 56,842 (3.5%) breast cancer survivors. Compared with women without breast cancer, breast cancer survivors were 6 years older (mean age 77 vs 71 years, P < .001), had significantly higher prevalence of dyslipidemia and hypertension, and lower prevalence of obesity, diabetes mellitus, and smoking. Breast cancer survivors were more likely to have a non-ST segment elevation acute myocardial infarction and less likely to receive mechanical revascularization. In-hospital mortality was lower in breast cancer survivors (7.1%) compared with those without (7.9%, P < .001), findings that persisted after risk adjustment (odds ratio 0.89; 95% CI, 0.82-0.94).

CONCLUSIONS

Breast cancer survivors had a first acute myocardial infarction at an older age and had small but favorable differences in cardiovascular disease risk factors and outcomes compared with women without breast cancer. The favorable impact of health education, preventative medical care, greater motivation for a healthier lifestyle, and participation in cancer survivorship programs on these seemingly paradoxical findings in breast cancer survivors should be further explored.

Cardiometabolic Effects of Endocrine Treatment of Estrogen Receptor-Positive Early Breast Cancer

Estrogen receptor-positive early breast cancer is common and has a relatively good prognosis. It shares risk factors with cardiovascular disease, and cardiovascular disease is an important competing cause of mortality. Adjuvant endocrine therapy with aromatase inhibitors (requiring concomitant ovarian suppression in premenopausal women) or selective estrogen receptor modulators (usually tamoxifen) exert oncologic benefits by respectively inhibiting estradiol synthesis or breast estrogen receptor signaling. Aromatase inhibitors cause systemic estradiol depletion. Tamoxifen has mixed agonistic/antagonistic effects in a tissue-dependent fashion. Given that estrogens modulate cardiometabolic risk, a review of the effects of endocrine therapy on cardiometabolic outcomes is pertinent. The current, but limited, evidence suggests that tamoxifen treatment, although associated with increases in body fat, hepatic steatosis, serum triglycerides, and diabetes risk, modestly reduces low-density lipoprotein cholesterol and lipoprotein(a) and may have favorable effects on markers of subclinical atherosclerosis. Tamoxifen is associated with either no effect on, or a reduction in, cardiovascular events, and it is associated with an increase in venous thromboembolic events. Aromatase inhibitors, although fewer studies are available and often confounded by comparison with tamoxifen, have not been consistently associated with adverse changes in cardiometabolic risk factors or increases in cardiovascular events. Further clinical trials designed to evaluate cardiometabolic outcomes are needed to more accurately determine the effects of endocrine therapy on cardiovascular risks, to inform individualized decisions regarding choice and duration of endocrine therapy, and to implement evidence-based strategies to mitigate cardiometabolic risks. In the meantime, although breast cancer-specific evidence for benefit of lifestyle measures is available and recommended routinely, proactive monitoring and treatment of cardiovascular risk factors should follow general population recommendations.

Association between tamoxifen use and acute myocardial infarction in women with breast cancer

The relationship between tamoxifen use and acute myocardial infarction in women with breast cancer remains uncertain. The goal of the study was to assess whether tamoxifen use could be associated with acute myocardial infarction in women with breast cancer in Taiwan.A population-based case-control study was conducted to analyze the database of the Taiwan National Health Insurance Program. Totally, 489 women with breast cancer aged 20 to 84 years having the first episode of acute myocardial infarction from 2000 to 2011 were found as the cases. In addition, 1718 women with breast cancer aged 20 to 84 years without any type of ischemic heart disease were selected as the matched controls. Ever use of tamoxifen was classified as the studied women who had at least a prescription for tamoxifen before the index date. Never use of tamoxifen was classified as the studied women who never had a prescription for tamoxifen before the index date. We used the multivariable logistic regression model to estimate the odds ratio (OR) and 95% confidence interval (CI) for acute myocardial infarction associated with tamoxifen use.In a multivariable-adjusted analysis, women with acute myocardial infarction were 1.71 times more likely to be exposed to tamoxifen than those women without acute myocardial infarction (adjusted OR 1.71, 95% CI 1.38-2.13).The odds of tamoxifen use are 1.71 times higher in women with acute myocardial infarction versus those women without acute myocardial infarction in Taiwan.

Antiplatelet Therapy in Breast Cancer Patients Using Hormonal Therapy: Myths, Evidence and Potentialities - Systematic Review

Breast cancer is the most frequently diagnosed tumor in women worldwide, with a significant impact on morbidity and mortality. Chemotherapy and hormone therapy have significantly reduced mortality; however, the adverse effects are significant. Aspirin has been incorporated into clinical practice for over 100 years at a low cost, making it particularly attractive as a potential agent in breast cancer prevention and as an adjunct treatment to endocrine therapy in the prophylaxis of cardiovascular complications. The objective of this study was to evaluate the role of aspirin in reducing the incidence of breast cancer and to evaluate the impact of its use on morbidity and mortality and reduction of cardiovascular events as adjuvant therapy during breast cancer treatment with selective estrogen receptor modulators. A systematic review was performed using the PRISMA methodology and PICO criteria, based on the MEDLINE, EMBASE and LILACS databases. The original articles of clinical trials, cohort, case-control studies and meta-analyses published from January 1998 to June 2017, were considered. Most studies showed an association between the use of selective estrogen receptor modulators and the increase in thromboembolic events. The studies suggest a protective effect of aspirin for cardiovascular events during its concomitant use with selective estrogen receptor modulators and in the prevention of breast cancer. This systematic review suggests that aspirin therapy combines the benefit of protection against cardiovascular events with the potential reduction in breast cancer risk, and that the evaluation of the benefits of the interaction of endocrine therapy with aspirin should be further investigated.

Long term adjuvant endocrine therapy and risk of cardiovascular disease in female breast cancer survivors: systematic review

OBJECTIVE

To investigate the effect of endocrine therapies on a wide range of specific clinical cardiovascular disease outcomes in women with a history of non-metastatic breast cancer.

DESIGN

Systematic review and meta-analysis of randomised controlled trials and observational studies.

DATA SOURCES

Medline and Embase up until June 2018.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

Studies were included if they investigated the risk of a specific cardiovascular disease outcome associated with use of either tamoxifen or an aromatase inhibitor, or compared the two treatments, in women with a history of non-metastatic breast cancer.

APPRAISAL AND DATA EXTRACTION

Relevant studies were originally identified and results extracted by one researcher, with a full replication of the study identification process by a combination of two other researchers. The Cochrane Collaboration's tool for assessing risk of bias was used to assess risk of bias in randomised controlled trials, and this tool was adapted to assess risk of bias in observational studies.

RESULTS

26 studies were identified, with results for seven specific cardiovascular disease outcomes (venous thromboembolism, myocardial infarction, stroke, angina, heart failure, arrhythmia, and peripheral vascular disease). Results suggested an increased risk of venous thromboembolism in tamoxifen users compared with both non-users and aromatase inhibitor users. Results were also consistent with a higher risk of the vascular diseases myocardial infarction and angina in aromatase inhibitor users compared with tamoxifen users, but there was also a suggestion that this may be partly driven by a protective effect of tamoxifen on these outcomes. Data were limited, and evidence was generally inconsistent for all other cardiovascular disease outcomes.

CONCLUSION

This review has collated substantial randomised controlled trial and observational evidence on the effect of endocrine therapies on several specific cardiovascular disease outcomes including venous thromboembolism and myocardial infarction, progressing knowledge. Although the choice of aromatase inhibitor or tamoxifen will primarily be based on the effectiveness against the recurrence of breast cancer, this review shows that the individual patient's risk of venous or arterial vascular disease should be an important secondary consideration.

SYSTEMATIC REVIEW REGISTRATION

Prospero CRD42017065944.

Long-Term Cardiovascular Risk After Radiotherapy in Women With Breast Cancer

Background

Radiotherapy for breast cancer often involves some incidental exposure of the heart to ionizing radiation. The effect of this exposure on the subsequent risk of heart disease is uncertain. We performed a meta‐analysis to investigate the link between radiotherapy and long‐term cardiovascular morbidity and mortality in patients with breast cancer.

Methods and Results

We performed a literature search using MEDLINE (January 1966 to January 2015) and EMBASE (January 1980 to January 2015) with no restrictions. Studies that reported relative risk (RR) estimates with 95%CIs for the associations of interest were included. Pooled effect estimates were obtained by using random‐effects meta‐analysis. Thirty‐nine studies involving 1 191 371 participants were identified. Patients who received left‐sided radiotherapy, as compared with those receiving right‐sided radiotherapy, experienced increased risks of developing coronary heart disease (RR 1.29, 95%CI 1.13‐1.48), cardiac death (RR 1.22, 95%CI 1.08‐1.37) and death from any cause (RR 1.05, 95%CI 1.01‐1.10). In a comparison of patients with radiotherapy and without radiotherapy, the RRs were 1.30 (95%CI 1.13‐1.49) for coronary heart disease and 1.38 (95%CI 1.18‐1.62) for cardiac mortality. Radiotherapy for breast cancer was associated with an absolute risk increase of 76.4 (95%CI 36.8‐130.5) cases of coronary heart disease and 125.5 (95%CI 98.8‐157.9) cases of cardiac death per 100 000 person‐years. The risk started to increase within the first decade for coronary heart disease and from the second decade for cardiac mortality.

Conclusions

Exposure of the heart to ionizing radiation during radiotherapy for breast cancer increases the subsequent risk of coronary heart disease and cardiac mortality.

The use of concurrent hormonotherapy and radiotherapy does not deteriorate radiation-induced cardiac toxicity

Postmenopausal patients with breast cancer have two options for adjuvant endocrine therapy, tamoxifen and aromatase inhibitors (AIs) as well as radiotherapy (RT) and chemotherapy. However, there is limited data regarding the optimal sequencing of RT and tamoxifen/AIs. Thus, we aimed to evaluate the effects of tamoxifen and AIs on radiation-induced cardiotoxicity. Eighty ovariectomized rats were divided into eight groups (G). G1 was defined as a control group; G2, G3, G4, and G5 were RT, tamoxifen, anastrozle, and letrozole groups, respectively; G6, G7, and G8 were RT plus tamoxifen, anastrozle, and letrozole groups, respectively. Drugs were started 1 week before RT and continued until the animals were killed 16 weeks after RT. The heart tissues were then dissected and examined with light microscopy to determine endocardial thickness and cardiac fibrosis. The endocardial thickness scores of both RT alone and the tamoxifen groups as well as the cardiac fibrosis score of RT alone were higher than that the control group ( p < 0.05 for all). There was no difference in the endocardial thickness and cardiac fibrosis scores of the RT-only group and the RT plus hormonotherapy groups ( p > 0.05 for all). Concurrent administration of RT and hormonal therapy with either tamoxifen or AIs did not further amplify radiation-induced cardiac toxicity. This issue warrants further study.

Adjuvant aromatase inhibitor therapy: outcomes and safety

Adjuvant therapy with the third-generation aromatase inhibitors (AIs) anastrozole, letrozole, and exemestane has largely replaced the use of tamoxifen (TAM) as standard adjuvant endocrine treatment for postmenopausal women with hormone-sensitive early breast cancer. Treatment strategies investigated in large, randomized, well-controlled clinical studies include the use of an AI as an upfront replacement for TAM, as an alternative to continued treatment with TAM, and in the extended adjuvant setting after at least 5 years of TAM. The efficacy of AIs over TAM has been demonstrated, particularly in terms of improving disease-free survival (DFS), and reductions in early distant metastasis with AIs may ultimately translate into improved overall survival. As AI therapy offers prolonged DFS, safety is an important concern over the long term. The AIs are better tolerated than TAM in terms of troublesome gynecologic adverse events such as vaginal bleeding and discharge, as well as life-threatening complications such as venous thromboembolic events and endometrial cancer. On the other hand, AI therapy has been associated with losses in bone density and a potential effect on lipids and cardiovascular risk. In trials comparing AIs with TAM, only limited conclusions can be made because of the putative cardioprotective, lipid-lowering, and bone-sparing effects of TAM. Studies comparing AIs with placebo, and/or in healthy women, may be more useful in understanding the long-term safety of adjuvant AI therapy. Results of ongoing safety analyses within some of the large AI trials should provide further insight into the long-term tolerability of AI therapy in the adjuvant setting.

Tamoxifen treatment in Danish breast cancer patients and 5-year risk of arterial atherosclerotic events: a null association

Although the effectiveness of tamoxifen in preventing the recurrence of breast cancer is well established, associations between tamoxifen and the occurrence of atherosclerotic events are not as clear. Breast cancer patients taking tamoxifen have lower serum cholesterol and other lipid levels than those not taking tamoxifen, suggesting that tamoxifen might prevent atherosclerotic events, but the existing studies are conflicting. We examined the relation between tamoxifen and incident hospitalization of angina pectoris, acute myocardial infarction, heart failure, and stroke. The study population of 16,289 women was identified from the Danish Breast Cancer Cooperative Group nationwide clinical database and includes women diagnosed with stage I or II estrogen receptor-positive breast cancer between 1990 and 2004 at ages 45 to 69. Use of a large population-based sample with complete outcome ascertainment allowed us to calculate precise measures of risks, risk ratios, and adjusted hazard ratios comparing tamoxifen-treated patients with untreated patients. We found strong evidence for null associations for each of the four outcomes of interest during the first year and first 5 years after the start of therapy. These findings are important in risk/benefit analyses as tamoxifen therapy in postmenopausal women is being replaced with aromatase inhibitors.

Translating trial data into patients benefits: making the right choice

Tamoxifen has been the standard first-line adjuvant treatment for postmenopausal women with early breast cancer for over 3 decades. Its use, however, is associated with a number of potentially life-threatening adverse events. As a result, the aromatase inhibitors (AIs), which are generally better tolerated and more efficacious, are now beginning to supersede tamoxifen as the treatment of choice in this setting. Nevertheless, some patients in clinical practice still start or remain on tamoxifen therapy instead of an AI. This review investigates our current understanding of AIs and tamoxifen in the adjuvant hormonal therapy of postmenopausal breast cancer in relation to efficacy, safety and patient benefits. Overall, it is concluded that the AIs show a significant advantage over tamoxifen, with the greatest difference observed at 1-2 years after initiation of treatment. Therefore, using an AI at the earliest opportunity provides patients with the best option to prevent the recurrence and excess adverse events associated with tamoxifen.

Comprehensive side-effect profile of anastrozole and tamoxifen as adjuvant treatment for early-stage breast cancer: long-term safety analysis of the ATAC trial

BACKGROUND

The Arimidex (anastrozole), Tamoxifen, Alone or in Combination (ATAC) trial was designed to compare the efficacy and safety of anastrozole with tamoxifen as adjuvant treatment for postmenopausal women with early-stage breast cancer. After an extended follow-up beyond the 5 years of treatment, we aimed to assess the safety, tolerability, and risk-benefit indices of these compounds.

METHODS

We analysed postmenopausal women (mean age 64 years [SD 9]) with localised breast cancer randomly assigned to anastrozole (n=3125) or tamoxifen (n=3116). Efficacy measures, including death and risk-benefit indices, were analysed by intention to treat. Safety analyses were based on treatment first received (n=3092 for anastrozole and n=3094 tamoxifen). We calculated a risk-benefit analysis using the two global indices for the Women's Health Initiative and for Disease-Free Survival and Serious Adverse Events. This study is registered as an International Standard Randomised Controlled Trial, number ISRCTN18233230.

FINDINGS

At median follow-up of 68 months (range 1-93), treatment-related adverse events occurred significantly less often with anastrozole than with tamoxifen (1884 [61%] vs 2117 [68%]; p<0.0001), as did treatment-related serious adverse events (146 [5%] vs 277 [9%]; p<0.0001) and adverse events leading to withdrawal (344 [11%] vs 442 [14%]; p=0.0002). Patients given anastrozole had significantly fewer overall events for the Global Index of the Women's Health Initiative (744 [24%] vs 851 [27%]; hazard ratio 0.85 [95% CI 0.77-0.94], p=0.001) and the Global Index of Disease-Free Survival and Serious Adverse Events (1453 [46%] vs 1594 [51%]; 0.88 [0.82-0.94]; p=0.0004).

INTERPRETATION

Anastrozole is tolerated better than tamoxifen by postmenopausal women with early-stage breast cancer, and results in fewer serious adverse events. Furthermore, it has a more favourable overall risk-benefit profile and lower recurrence rate than tamoxifen.

Coronary heart disease and stroke with aromatase inhibitor, tamoxifen, and menopausal hormone therapy use

Results from the Women's Health Initiative randomized clinical trials of hormone therapy provide the clinical context for interpreting tamoxifen and aromatase inhibitor (AI) findings regarding coronary heart disease (CHD) and stroke. Of note is the potential link between increased stroke risk and increased dementia risk seen with the use of estrogen alone and the combination of estrogen/progestin. Like hormone therapy, tamoxifen has been found to generally lower low-density lipoprotein and total cholesterol but increase triglyceride levels. The preponderance of clinical evidence suggests that tamoxifen increases stroke risk and has no effect or modestly reduces CHD risk. Aromatase inhibitors generally do not influence low-density lipoprotein cholesterol and could modestly increase high-density lipoprotein cholesterol and reduce triglyceride levels. Current but limited evidence suggests that AIs have a modest increase or no effect on CHD as a class or as individual agents compared with tamoxifen. The influence of AIs on stroke is unsettled, and within-class differences might exist. In the adjuvant breast cancer setting, based on available evidence, the influence of AIs on CHD or stroke will infrequently influence overall patient outcome. If remaining issues are to be addressed, more rigorous CHD and stroke assessment procedures are needed in future trials evaluating AIs.

Anastrozole as an adjuvant endocrine treatment for postmenopausal patients with breast cancer: emerging data

The Arimidex, Tamoxifen, Alone or in Combination (ATAC) trial compared the efficacy and safety of anastrozole versus tamoxifen versus the combination as initial adjuvant treatment for early breast cancer in over 9,000 postmenopausal women. Analyses at 33 and 47 months median follow-up showed that anastrozole significantly prolonged disease-free survival and time to recurrence and reduced the incidence of contralateral breast cancer compared with tamoxifen. Results of the completed treatment analysis at 68 months median follow-up confirmed the earlier findings, showing that the absolute difference in disease-free survival continued to increase beyond completion of treatment. Mature safety data from the ATAC trial show that, overall, anastrozole has a favorable safety profile compared with tamoxifen. In the absence of current data on further follow-up or the outcome of trials investigating proactive sequencing of endocrine therapies, we present a model based on several trials, including ATAC. This model suggests that using an aromatase inhibitor as initial adjuvant therapy is a better option than switching to an aromatase inhibitor after >/=2 years of tamoxifen. The relative toxicities of the three approved third-generation aromatase inhibitors, anastrozole, letrozole, and exemestane, are discussed. These data suggest that long-term safety profiles may differ between aromatase inhibitors, although comprehensive comparative data for letrozole and exemestane versus tamoxifen are lacking.

Choosing between an aromatase inhibitor and tamoxifen in the adjuvant setting

PURPOSE OF REVIEW

Approximately three-quarters of all invasive breast tumors are estrogen and/or progesterone receptor-positive. The selective estrogen receptor modulator tamoxifen has been the preferred endocrine therapy for almost four decades. One of the most significant advances in endocrine therapy for women after menopause with early breast cancer is the introduction of third-generation aromatase inhibitors as an alternative or as an additional treatment to tamoxifen therapy. In making a choice between the use of an aromatase inhibitor or tamoxifen in the adjuvant setting, a careful analysis of both the efficacy data and toxicity profiles of each drug is essential.

RECENT FINDINGS

In the adjuvant setting, three major randomized controlled trials have reported on the use of three different aromatase inhibitors for women after menopause with breast cancer. In all of these trials, the third-generation aromatase inhibitors demonstrated significantly improved disease-free survival, either compared with tamoxifen as an initial adjuvant hormonal therapy, or when aromatase inhibitors were given sequentially after tamoxifen therapy. The toxicity data suggest that bone loss, increased fracture rates, and other musculoskeletal disorders are the most serious side effects associated with the use of aromatase inhibitors. Toxicities commonly associated with tamoxifen therapy such as thromboembolic events and endometrial abnormalities are reduced in patients receiving aromatase inhibitors, however.

SUMMARY

The present data demonstrate the improved efficacy achieved with third-generation aromatase inhibitors compared with tamoxifen and support the use of these agents in the adjuvant setting. The optimal treatment strategy for whether these agents should be given in place of tamoxifen or as part of a sequential treatment has yet to be defined, however. Moreover, to be able to optimize treatment with aromatase inhibitors, it is imperative to develop interventions to prevent or alleviate treatment related side effects.