Defining the role of aromatase inhibitors in the adjuvant endocrine treatment of early breast cancer

Aromatase Inhibitors-Induced Musculoskeletal Disorders: Current Knowledge on Clinical and Molecular Aspects

Aromatase inhibitors (AIs) have radically changed the prognosis of hormone receptor positive breast cancer (BC) in post-menopausal women, and are a mainstay of the adjuvant therapy for BC after surgery in place of, or following, Tamoxifen. However, AIs aren't side effect-free; frequent adverse events involve the musculoskeletal system, in the form of bone loss, AI-associated arthralgia (AIA) syndrome and autoimmune rheumatic diseases. In this narrative review, we reported the main clinical features of these three detrimental conditions, their influence on therapy adherence, the possible underlying molecular mechanisms and the available pharmacological and non-pharmacological treatments. The best-known form is the AIs-induced osteoporosis, whose molecular pathway and therapeutic possibilities were extensively investigated in the last decade. AIA syndrome is a high prevalent joint pain disorder which often determines a premature discontinuation of the therapy. Several points still need to be clarified, as a universally accepted diagnostic definition, the pathogenetic mechanisms and satisfactory management strategies. The association of AIs therapy with autoimmune diseases is of the utmost interest. The related literature has been recently expanded, but many issues remain to be explored, the first being the molecular mechanisms.

Recent developments in steroidal and nonsteroidal aromatase inhibitors for the chemoprevention of estrogen-dependent breast cancer

Aromatase, a cytochrome P450 enzyme complex present in breast tissues, plays a significant role in the biosynthesis of important endogenous estrogens from androgens. The source of estrogen production in breast cancer tissues is intra-tumoral aromatase, and inhibition of aromatase may inhibit the growth stimulation effect of estrogens in breast cancer tissues. Consequently, aromatase is considered a useful therapeutic target in the treatment and prevention of estrogen-dependent breast cancer. Recently, different natural products and synthetic compounds have been rapidly developed, studied, and evaluated for aromatase inhibitory activity. Aromatase inhibitors are classified into two categories on the basis of their chemical structures, i.e., steroidal and nonsteroidal aromatase inhibitors. This review highlights the synthetic steroidal and nonsteroidal aromatase inhibitors reported in the literature in the last few years and will aid medicinal chemists in the design and synthesis of novel and pharmacologically-potent aromatase inhibitors for the treatment of breast cancer.

Progesterone receptor A predominance is a discriminator of benefit from endocrine therapy in the ATAC trial

Progesterone receptor (PR) function, while essential in normal human breast, is also implicated in breast cancer risk. The two progesterone receptors, PRA and PRB, are co-expressed at equivalent levels in normal breast, but early in carcinogenesis normal levels of PRA:PRB are frequently disrupted, and predominance of one isoform, usually PRA, results. In model systems, PRA and PRB have different activities, and altering the PRA:PRB ratio in cell lines alters PR signaling. The purpose of this study was to determine whether hormonal or reproductive factors contribute to imbalanced PRA:PRB expression in breast tumors and the impact of PRA:PRB imbalance on disease outcome. The relative expression of PRA and PRB proteins was determined by dual immunofluorescence histochemistry in archival breast tumors and associations with clinical and reproductive history assessed. PRA:PRB expression was not influenced by reproductive factors, whereas exogenous hormone use (menopausal hormone treatment, MHT) favored PRB expression (p < 0.035). The PRA:PRB ratio may be a discriminator of response to endocrine therapy in the TransATAC sample collection, with high PRA:PRB ratio predicting earlier relapse for women on tamoxifen, but not anastrozole (mean lnPRA:PRB ratio; HR (95 % CI) tamoxifen 2.45 (1.20-4.99); p value 0.02; anastrozole 0.80 (0.36-1.78); p value 0.60). The results of this study show that PRA:PRB imbalance in breast cancers is not associated with lifetime endogenous endocrine and reproductive factors, but is associated with MHT use, and that PRA predominance can discriminate those women who will relapse earlier on tamoxifen treatment. These data support a role for imbalanced PRA:PRB expression in breast cancer progression and relative benefit from endocrine treatment.

[Towards an integrated approach to cardiovascular toxicities related to the treatments of breast cancer]

There is an increasing number of therapeutic options in breast cancer management. While prognosis improves, the cardiac toxicity related to treatments remains a significant issue. This toxicity has several clinical presentations and can be explained by complex and diverse molecular mechanisms. Systemic treatments (anthracyclines, inhibitors of HER2 signaling pathway, hormone therapy, antiangiogenic agents) and radiotherapy have their own cardiac toxicity. However, the toxicities associated with these treatments may potentiate together and the existence of pre-existing cardiovascular risk factors should be taken into account. The assessment of cardiac hazard evolves toward a multifactorial approach. Several possibilities exist to minimize the incidence of cardiac complications. Those include pharmacological and technological innovations, but also a more accurate selection of patients and a growing involvement of practitioners in the field of cardiac toxicity, which is prerequisite for an early management of cardiac events.

Efficacy of a combined alendronate and calcitriol agent (Maxmarvil®) in Korean postmenopausal women with early breast cancer receiving aromatase inhibitor: a double-blind, randomized, placebo-controlled study

The use of aromatase inhibitor (AI) in postmenopausal women with hormone receptor (HR)-positive early breast cancer (EBC) produces a deleterious effect on bone mass and an increase in fractures. Several studies using intravenous bisphosphonates have shown effective management of AI-induced bone loss. To determine whether a lower dosage in oral form combined with calcitriol can effectively manage AI-induced bone loss, we performed a randomized, double-blind, prospective, placebo-controlled 24-week trial with a combination of alendronate and 0.5-µg of calcitriol daily to HR-positive EBC patients. A total of 98 Korean postmenopausal women with HR-positive EBC who received daily AI, calcium and vitamin D were randomly assigned to 5-mg of alendronate and 0.5-µg of calcitriol (Maxmarvil®) or placebo groups. The bone mineral density (BMD) and turnover markers were measured. At week 24, the difference in lumbar BMD between the groups was 3.0% (p < 0.005). The increase in C-telopeptide after 24 weeks was significantly less in the Maxmarvil group compared to that in the placebo group (35.2 ± 17.5% vs. 109.8 ± 28.6%, p < 0.05). Our study demonstrates that a combination of 5-mg alendronate and 0.5-µg calcitriol is effective to prevent bone loss due to AI in Korean postmenopausal women with EBC.

Current role and safety profile of aromatase inhibitors in early breast cancer

The current adjuvant therapy for breast cancer is in a continous progress; standard therapeutic strategies include the use of chemotherapy, molecular targeted drugs and hormonal agents, according to well-established prognostic and predictive factors. Among the hormonal drugs, for a long period tamoxifen has been the gold standard of adjuvant therapy in postmenopausal women with hormone receptor-positive (HR+) early breast cancer. In the last years an expanding use of aromatase inhibitors occurred in this subset of patients, because the third-generation class of these agents (anastrozole, letrozole and exemestane) showed to be more effective and safe than tamoxifen and are now recommended as the preferred hormonal approach to postmenopausal hormone-sensitive patients, according to national and international guidelines. Treatment choices with these agents include the use of an aromatase inhibitor as an upfront strategy for 5 years, as a sequential approach after 2-3 years of tamoxifen, or as an extended use after the classical 5 years of tamoxifen. The improved efficacy of aromatase inhibitors over tamoxifen has been largely demonstrated in terms of better disease-free survival, reductions in the occurrence of early distant metastasis as well as improvement of overall survival. Moreover, according to the optimal duration of therapy, presently it is not known whether aromatase inhibitor therapy, as tamoxifen, should be limited to 5 years. In terms of safety profile, the side effects of aromatase inhibitors, as compared with selective estrogen receptor modulators, are different, reflecting the specific mechanism of action of these drugs. There is strong evidence that aromatase inhibitors are well tolerated, with a lower incidence of gynecological symptoms (vaginal bleeding, discharge and endometrial neoplasia), venous thromboembolic events and hot flushes than tamoxifen. On the other hand, the use of aromatase inhibitors has been associated with loss of bone density, arthralgia, myalgia, and a negative effect on lipid metabolism and cardiovascular risk. More extensive and mature studies are necessary to well establish the safety of aromatase inhibitors when given to patients with breast cancer for a long time.

Minimizing early relapse and maximizing treatment outcomes in hormone-sensitive postmenopausal breast cancer: efficacy review of AI trials

Breast cancer is one of the leading causes of cancer-related deaths in women. Regardless of prognosis, all women with breast cancer are at risk for early recurrence. Nearly 50% of early recurrences occur within 5 years of surgery, and they peak at 2 years after surgery in women treated with adjuvant tamoxifen. Most early recurrences are distant metastases, which strongly correlate with increased mortality. Treatments that mitigate the risk of early distant metastases (DM) are, therefore, likely to improve overall survival in women with early breast cancer (EBC). Aromatase inhibitors (AIs)--anastrozole, letrozole, and exemestane-have been investigated as alternatives to tamoxifen for adjuvant treatment of hormone receptor-positive (HR+) EBC in postmenopausal women (PMW). AIs are better at minimizing risk of early relapse compared with tamoxifen. However, it is not clear if preferential use of AIs over tamoxifen will benefit all PMW with HR+ EBC. The ability to subtype HR+ breast cancer on the basis of biomarkers predictive of response to AIs and tamoxifen would likely be key to determining the most beneficial hormonal treatment within patient subpopulations, but this process requires thorough investigation. Until then, adjuvant therapies that provide the greatest reduction in risk of DM should be considered for all PMW with HR+ EBC. This article reviews the clinical trials of AI adjuvant therapies for hormone-sensitive breast cancer, particularly in the context of how they compare with tamoxifen in minimizing the risk of relapse, occurrence of DM, and breast cancer-related deaths.

Cardiac toxicity in breast cancer patients: from a fractional point of view to a global assessment

When focusing on heart disease, most available studies split the two different parts of the adjuvant treatment, i.e., systemic therapies and radiation therapy, making it difficult to implement efficient strategies for preventing treatment-induced cardiac toxicity. This paper reviews the current understanding of treatments-induced cardiac toxicity in a global approach. Many factors should be considered when assessing the cardiac hazard. Treatment-related risk factors include heart dose exposure, chemotherapy, targeted agents such as HER2 inhibitors, but also endocrine agents, or anesthetic procedure. Patients' characteristics should also be taken into account. Age, menopausal status, stress, previous history of cardiac disease, genetic profile, and body mass index could all impact on cardiac function after adjuvant therapies. Cardiac toxicity should not be analyzed as the consequence of a specific therapy, but should be considered as the result of additive or supra-additive toxicities. By this way, it will be possible to implement new strategies for preventing treatment-induced cardiac toxicity.

Prevention of Aromatase Inhibitor–Induced Bone Loss Using Risedronate: The SABRE Trial

Purpose

To investigate the management of bone health in women with early breast cancer (EBC) who were scheduled to receive anastrozole.

Patients and Methods

Postmenopausal women with hormone receptor–positive EBC were assigned to one of three strata by risk of fragility fracture. Patients with the highest risk (H) received anastrozole 1 mg/d plus risedronate 35 mg/wk orally. Patients with moderate-risk (M) were randomly assigned in a double-blind manner to anastrozole and risedronate (A + R) or to anastrozole and placebo (A + P). Patients with lower-risk (L) received anastrozole (A) alone. Calcium and vitamin D were recommended for all patients. Lumbar spine and total hip bone mineral density (BMD) were assessed at baseline, 12 months, and 24 months.

Results

At 24 months, in the M group, treatment with A + R resulted in a significant increase in lumbar spine and total hip BMD compared with A + P treatment (2.2% v −1.8%; treatment ratio, 1.04; P < .0001; and 1.8% v −1.1%; treatment ratio, 1.03; P < .0001, respectively). In the H stratum, lumbar spine and total hip BMD increased significantly (3.0%; P = .0006; and 2.0%; P = .0104, respectively). Patients in the L stratum showed a significant decrease in lumbar spine BMD (−2.1%; P = .0109) and a numerical decrease in total hip BMD (−0.4%; P = .5988). Safety profiles for anastrozole and risedronate were similar to those already established.

Conclusion

In postmenopausal women at risk of fragility fracture who were receiving adjuvant anastrozole for EBC, the addition of risedronate at doses established for preventing and treating osteoporosis resulted in favorable effects in BMD during 24 months.

Safety, tolerability and pharmacokinetics of TAS-108, a novel anti-oestrogen, in healthy post-menopausal Japanese women: a phase I single oral dose study

TAS-108 is a novel steroidal anti-oestrogen, expected to be useful for the treatment of breast cancer. The present study was conducted to investigate the safety, tolerability and pharmacokinetics of TAS-108 following the administration at a single oral dose of 40 mg to up to 120 mg in 12 post-menopausal women and the effect of food on the pharmacokinetics of the drug. All adverse events were mild and involved transient symptoms that resolved without therapeutic intervention. TAS-108 was readily absorbed and plasma levels of TAS-108 steadily declined, apparently in a multi-exponential manner. C(max) and AUC(0-12) were proportionally increased with increasing dose of TAS-108. The C(max) and AUC(0-t) of TAS-108 and its metabolite, deEt-TAS-108, were significantly increased to approximately 150% when TAS-108 was administered after a meal. Food did not affect the elimination half-life of TAS-108 or its metabolites. In this escalating dose-study of TAS-108, the drug was well tolerated by healthy post-menopausal Japanese women. The pharmacokinetics of TAS-108 indicated dose proportionality, and its bioavailability was significantly increased by food intake.

Initial treatment and changes in adjuvant endocrine therapy for early stage breast cancer

Clinical trials have shown that aromatase inhibitors (AIs) are an important advance in the treatment of early stage breast cancer (ESBC), but practice patterns and the impact of treatment side effects of endocrine therapy in the community setting have not been extensively explored. This retrospective chart review describes practice patterns among patients receiving adjuvant endocrine therapy for ESBC. Charts of 200 patients with confirmed stage I-IIIA breast cancer were reviewed. Patients received first-line treatment with tamoxifen (n=96) or AIs (n=104). Fifty-one patients completed a structured interview regarding symptom burden during therapy. Time to discontinuation or switching from first-line therapy did not vary by drug class (tamoxifen vs. AI). Musculoskeletal symptoms predicted time to switching among AI patients. Tamoxifen patients who switched to AIs tended to do so following clinical guidelines for use of AIs. Interview results showed that more anastrozole than tamoxifen patients cited side effects as the reason for switching.

Meta-analysis of trials comparing anastrozole and tamoxifen for adjuvant treatment of postmenopausal women with early breast cancer

OBJECTIVE

It was aimed to review the literature and make a meta-analysis of the trials on both upfront, switching, and sequencing anastrozole in the adjuvant treatment of early breast cancer.

METHODS

The PubMed, ClinicalTrials.gov and Cochrane databases were systematically reviewed for randomized-controlled trials comparing anastrozole with tamoxifen in the adjuvant treatment of early breast cancer.

RESULTS

The combined hazard rate of 4 trials for event-free survival (EFS) was 0.77 (95%CI: 0.70-0.85) (P < 0.0001) for patients treated with anastrozole compared with tamoxifen. In the second analysis in which only ITA, ABCSG 8, and ARNO 95 trials were included and ATAC (upfront trial) was excluded, combined hazard rate for EFS was 0.64 (95%CI: 0.52-0.79) (P < 0.0001). In the third analysis including hazard rate for recurrence-free survival (excluding non-disease related deaths) of estrogen receptor-positive patients for ATAC trial and hazard rate for EFS of all patients for the rest of the trials, combined hazard rate was 0.73 (95%CI: 0.65-0.81) (P < 0.0001).

CONCLUSION

Anastrozole appears to have superior efficacy than tamoxifen in the adjuvant hormonal treatment of early breast cancer. Until further clinical evidence comes up, aromatase inhibitors should be the initial hormonal therapy in postmenopausal early breast cancer patients and switching should only be considered for patients who are currently receiving tamoxifen.

Effect of raloxifene on mammographic density and breast magnetic resonance imaging in premenopausal women at increased risk for breast cancer

BACKGROUND

Mammographic density is a risk factor for breast cancer. Mammographic density and breast magnetic resonance imaging (MRI) volume (MRIV) assess the amount of fibroglandular tissue in the breast. Mammographic density and MRIV can be modulated with hormonal interventions, suggesting that these imaging modalities may be useful as surrogate endpoint biomarkers for breast cancer chemoprevention trials. We evaluated the effect of raloxifene on mammographic density and MRIV in premenopausal women at increased risk for breast cancer.

METHODS

Mammograms and MRI were obtained at baseline and after 1 and 2 years of 60 mg raloxifene by mouth daily for 27 premenopausal women. Mammographic percent dense area was calculated using a semiquantitative thresholding technique. T(1)-weighted spoiled gradient-echo MRI with fat suppression was used to determine breast MRIV using a semiautomatic method. Mean change in mammographic density and median change in MRIV were assessed by the Wilcoxon signed-rank test.

RESULTS

No significant change in mammographic density was seen after treatment with raloxifene. Mean change after 1 year was 1% [95% confidence interval (95% CI), -3 to +5] and after 2 years was 1% (95% CI, -2 to +5). MRIV decreased on raloxifene. Median relative change in MRIV after 1 year was -17% (95% CI, -28 to -9; P = 0.0017) and after 2 years was -16% (95% CI, -31 to -4; P = 0.0004).

CONCLUSIONS

In high-risk premenopausal women, mammographic density did not change on raloxifene, whereas MRIV significantly declined. Our findings suggest that MRIV is a promising surrogate biomarker in premenopausal women at increased risk for breast cancer and should be investigated further in breast cancer prevention trials.

Effects of third generation aromatase inhibitors on bone health and other safety parameters: results of an open, randomised, multi-centre study of letrozole, exemestane and anastrozole in healthy postmenopausal women

Given potential differences between the skeletal and other effects of the third generation aromatase inhibitors (AIs), we conducted an open, randomised Phase I study, comparing the effects of three licensed AIs on bone turnover markers, lipid profiles and adrenal function. Treatment comparisons were undertaken in 90 healthy postmenopausal women with normal bone mineral density who received once daily oral anastrozole (1mg, n=29), letrozole (2.5mg, n=29) or exemestane (25mg, n=32) for 24weeks with a subsequent 12week washout period. All three AIs induced increases in bone resorption markers, but no significant differences were observed in their effects on bone turnover markers. Greater differences were observed in lipid metabolism. Notably, exemestane, but not anastrozole or letrozole, significantly increased the LDL:HDL cholesterol ratio by 12weeks, largely mediated by a decrease in HDL-cholesterol. Further, long-term clinical studies are required to determine the impact, if any, of the differences observed between the AIs

Aromatase inhibitor-induced arthralgia: clinical experience and treatment recommendations

It is well documented that the aromatase inhibitors (AIs) are superior to tamoxifen as adjuvant endocrine therapy in postmenopausal women with hormone receptor-positive breast cancer. However, compared with tamoxifen, an elevated incidence of arthralgia has been observed during AI treatment. Concerns have been raised that AI-induced arthralgia may dissuade patients from completing their full AI treatment course, and may also deter physicians from prescribing an AI if they feel that patients may be at risk of permanent joint damage. Patient education about the possibility of experiencing arthralgia, and effective management of symptoms if they appear, are important in helping patients adhere to AI treatment, and consequently improving breast cancer outcomes. In this paper, we discuss the potential mechanisms behind AI-induced arthralgia, review the frequency with which arthralgia occurs, and propose for the first time an algorithm specifically for the treatment of AI-induced arthralgia. As with joint pain in non-breast cancer patients, a sequential approach to disease management is recommended, involving modifying the patient's lifestyle in addition to taking a stratified approach to pharmacological intervention with analgesia and anti-inflammatory medication. Knowing that joint symptoms can be managed in most patients may encourage patient-physician communication and treatment compliance.

Aromatase inhibitors: past, present and future in breast cancer therapy

Estrogen has been implicated in promoting breast cancer in a majority of women. Endocrine therapy controlling estrogen production has been the guiding principle in treating breast cancer for more than a century. A greater understanding of this disease at a molecular level has led to the development of molecules that inhibit estrogen production by inhibiting the aromatase enzyme, that is the primary source of estrogen in postmenopausal women. This review examines the evolution of aromatase inhibitor (AI) based therapies over the past three decades. The third generation aromatase inhibitors (anastrozole, letrozole and exemestane), which have been found to be extremely specific and effective in an adjuvant/neoadjuvant/extended adjuvant setting are discussed from a biochemical and clinical perspective. A comprehensive discussion of the past, present, and future of aromatase inhibitors is conducted in this review.

Assessing the risk of bone fracture among postmenopausal women who are receiving adjuvant hormonal therapy for breast cancer

OBJECTIVE

To understand better the true impact of widespread adoption of adjuvant aromatase inhibitor (AI) therapy on postmenopausal breast cancer patients' risk of bone fracture.

METHODS

Data from three different studies were used to estimate the relative risk of bone fracture for each of the following groups of women (i.e., versus a control group of healthy postmenopausal women): (a) healthy postmenopausal women receiving tamoxifen; (b) postmenopausal women who had received treatment for early breast cancer; (c) postmenopausal breast cancer patients on adjuvant tamoxifen therapy; (d) postmenopausal breast cancer patients on adjuvant anastrozole therapy. The results of these analyses were then used to estimate the likely incidence of clinical fracture among such populations in 'real-life' clinical practice.

RESULTS

Breast cancer survivors were calculated to be at increased risk of clinical bone fracture (i.e., RR 1.15 vs. control group over 5 years). Breast cancer patients initiated on adjuvant anastrozole were also calculated to be at increased risk of bone fracture (RR = 1.36 vs. control group over 5 years), while the calculated risk of fracture among tamoxifen-treated breast cancer patients was similar to that observed in the control population (RR = 0.91).

CONCLUSION

Breast cancer patients are at increased risk of clinical bone fracture (compared with the general postmenopausal population) and adjuvant anastrozole therapy slightly adds to this risk. Importantly, however, the absolute risk of bone fracture appears to remain low in each of the evaluated patient populations, suggesting that fear of fracture should not prevent the initiation of adjuvant aromatase inhibitor therapy.

Aromatase inhibitors: a safety comparison

For almost three decades, tamoxifen has been the mainstay of hormonal therapy in breast cancer patients, but now the third-generation aromatase inhibitors (AIs), anastrozole, letrozole and exemestane, are emerging as potential alternatives, associating greater clinical efficacy with a more favourable overall safety profile than tamoxifen. AIs are associated with a lower incidence of thromboembolic events and vaginal bleeding compared with tamoxifen, although they are known to affect bone turnover and possibly lipid metabolism. As the available AIs have similar efficacy, it is likely that safety and tolerability profiles will have an impact on agent selection in clinical practice. Therefore, it is important that differences in the safety profiles of the third-generation AIs are understood.