Aromatase Inhibitors in Adjuvant Therapy of Breast Cancer: Before, Instead of, or Beyond Tamoxifen

Management of Bone Loss Induced by Aromatase Inhibitors

Aromatase inhibitors are quickly becoming standard adjuvant endocrine therapy for hormone-receptor positive breast cancer, either upfront or in sequence after tamoxifen. As other means of estrogen-depleting therapy, decreasing bone mineral density is the major side effect of this treatment. As increase in fracture incidence have already been reported in most major trials of aromatase inhibitors. Bisphosphonates are used to treat this cancer-treatment induced bone loss, the available data is reviewed here.

Reducing the risk of distant metastases: a better end point in adjuvant aromatase inhibitor breast cancer trials?

For women with hormone receptor-positive disease, the third-generation aromatase inhibitors (AIs), anastrozole, letrozole, and exemestane, are more effective than tamoxifen in improving disease-free survival (DFS) when used initially or as adjuvant therapy following two to three years of tamoxifen or after tamoxifen has been completed. Demonstrating improvement in overall survival (OS), or breast cancer-associated mortality, however, requires long follow-up in large numbers of patients. Subsequent crossover to another treatment following disease recurrence further confounds the assessment of OS benefit. DFS is the primary end point of most adjuvant trials, but the definition varies among trials, making cross-trial comparisons difficult. Importantly, DFS benefit does not always correlate with OS benefit. Distant metastasis is a well-recognized predictor of breast cancer-associated mortality, and AIs have shown greater efficacy over tamoxifen in reducing distant metastatic events and improving distant DFS (DDFS). A small proportion of initially treated early breast cancer patients may already have micrometastatic tumor deposits that can result in the rapid development of distant metastases. Thus, early identification and aggressive treatment of such patients with the most effective adjuvant therapies is a major goal. This review discusses the efficacy of the AIs in improving DDFS in the different adjuvant settings and explores whether significant improvements in DDFS correlate with meaningful improvements in OS or breast cancer-associated mortality. Significant DDFS improvement may be a quicker, better end point in clinical trials, leading to a more efficient, faster assessment of treatment efficacy.

Facilitating breast-conserving surgery and preventing recurrence: aromatase inhibitors in the neoadjuvant and adjuvant settings

Breast-conserving surgery (BCS) is an attractive option for many patients with early-stage breast cancer, because it provides a better cosmetic outcome than modified radical mastectomy, while reducing surgical morbidity. In patients with large, operable breast tumors who are ineligible for BCS, neoadjuvant therapy is a useful option for reducing the tumor size and for increasing the proportion of candidates for BCS. In patients with endocrine-responsive tumors, neoadjuvant endocrine therapy with either tamoxifen or an aromatase inhibitor (AI; anastrozole, letrozole, or exemestane) provides an alternative to neoadjuvant chemotherapy. Clinical trials have demonstrated the superiority of neoadjuvant AIs over tamoxifen in achieving a clinical response and increasing the frequency of BCS. In addition, adjuvant endocrine therapy with AIs, whether used as initial therapy instead of tamoxifen, in a switching strategy after 2-3 years of tamoxifen, or as extended adjuvant therapy after 5 years of adjuvant tamoxifen, has been shown in several randomized clinical trials to improve disease-free survival, reduce distant metastases and, in some cases, improve overall survival. The availability of the AIs for effective and well-tolerated neoadjuvant and/or adjuvant endocrine therapy represents an important advance in breast cancer treatment, and surgeons should be familiar with these new therapeutic options.

Treatment strategies that effectively reduce early recurrence risk in postmenopausal women with endocrine-sensitive breast cancer: AIs upfront vs. switching

Several large, well-controlled clinical trials have now established that the aromatase inhibitors (AIs), including letrozole, anastrozole, and exemestane, are more effective than tamoxifen when used as adjuvant endocrine therapy in postmenopausal women with breast cancer. Yet, it is an open question as to how these drugs should be best integrated into the adjuvant treatment regimen. Both letrozole and anastrozole have shown efficacy over tamoxifen when used as initial adjuvant therapy (initiated just following surgery for breast cancer), while exemestane and anastrozole have been used as switching adjuvant therapy, i.e., following 2-3 years of initial adjuvant tamoxifen therapy, with proven efficacy over continued tamoxifen. Studies demonstrate that recurrence risk peaks in the early period after surgery, and that distant metastases in particular, accounting for most of the early recurrences, have worse survival rates when compared with other types of recurrences. Treatments that reduce recurrences, especially distant metastases, in this early period are therefore likely to improve overall survival (OS) and reduce mortality from breast cancer. In this review, we discuss early recurrence risk among postmenopausal women with successfully treated early breast cancer, the efficacy of the different AIs in reducing early recurrences and distant metastases when incorporated into adjuvant therapy, and the evidence for increased OS when AIs are used as initial or switch adjuvant therapy.

The prevention and management of distant metastases in women with breast cancer

About one-third of all women diagnosed with breast cancer face the risk of recurrence, which can occur at any stage of disease, observation time, and after any treatment modality. Most recurrence comes in the form of distant metastasis, which is the major cause of death in women with breast cancer. Treatments shown to decrease the risk of breast cancer recurrence, especially distant metastasis, will likely produce a survival benefit and a potentially significant improvement in quality of life in women with early breast cancer. New third-generation aromatase inhibitors (anastrozole, exemestane, and letrozole) that have been shown to be well tolerated have the potential to contribute to benefits beyond those seen with tamoxifen.

Towards optimal endocrine therapy for hormone-sensitive breast cancer: Initial versus sequential adjuvant aromatase inhibition

Patients with hormone-receptor-positive early breast cancer have a significant risk of recurrence despite the use of adjuvant tamoxifen. The third-generation aromatase inhibitors letrozole, anastrozole, and exemestane offer promise as alternative or additional therapy to tamoxifen. As extended adjuvant therapy following completion of 5 years of tamoxifen, letrozole further decreased the risk of recurrence compared with placebo. Compared with tamoxifen, both letrozole and anastrozole significantly reduced the risk of recurrence when used as initial adjuvant therapy, and in the short term both were better tolerated than tamoxifen. Anastrozole and exemestane both reduced the risk of relapse when started after 2-3 years of tamoxifen compared with continued tamoxifen treatment; the results of letrozole in this setting are expected in 2008. These data establish adjuvant aromatase inhibitors as effective alternatives to tamoxifen. Only limited data are currently available to inform the choice between an aromatase inhibitor as either initial adjuvant therapy or sequentially after tamoxifen. Future results from the Breast International Group (BIG) 1-98 trial will further clarify strategies for the adjuvant use of aromatase inhibitors. Here, we critically review the evidence for adjuvant use of aromatase inhibitors. Comparison is made between initial aromatase inhibition, switching, and extended adjuvant strategies. Practical recommendations are given for the endocrine treatment of post-menopausal breast cancer.

Aromatase inhibitors in early breast cancer therapy: a variety of treatment strategies

Until recently, standard endocrine therapy for estrogen receptor-positive early breast cancer in the preoperative neoadjuvant and postoperative adjuvant settings was the selective estrogen receptor modulator tamoxifen. An alternate therapeutic approach is to suppress total-body estrogen synthesis using an aromatase inhibitor. The highly potent and specific third-generation aromatase inhibitors (anastrozole, exemestane and letrozole) have consistently demonstrated improved efficacy over tamoxifen in large randomised neoadjuvant and adjuvant clinical trials. As neoadjuvant therapy, compared with tamoxifen, all three aromatase inhibitors significantly improved breast-conserving surgery rates, but only letrozole achieved a significantly higher overall response rate. These agents have also been evaluated in three adjuvant strategies: instead of tamoxifen for 5 years, sequenced after 2-3 years of tamoxifen, or as extended adjuvant therapy following a full 5-year course of tamoxifen. In all cases, the aromatase inhibitor was significantly more effective in reducing the risk of recurrence, compared with tamoxifen in the first two approaches and with placebo or no treatment as extended therapy. Long-term aromatase inhibitor treatment is associated with less endometrial cancer, thromboembolic events and strokes than tamoxifen, but more musculoskeletal disorders and bone loss. Further investigation is focusing on identification of the patient subgroups most likely to benefit from each of these adjuvant therapy options.

Adjuvant therapy for patients who have node-positive breast cancer

The treatment of node-positive breast cancer has improved dramatically in the last 3 decades. Adjuvant therapies have evolved from single-agent chemotherapy to anthracycline- and taxane-based polychemotherapeutics to target-specific trastuzumab, with or without endocrine manipulation and with or without PMRT. Almost 85% of patients who have node-positive disease can now enjoy a 5-year DFS. This progress has come from incremental improvements made over the years. In spite of these advances, lingering questions remain. Is it possible to reduce treatment-associated toxicity? Can patient selection be improved based on tumor genomic profiling? Given the high cost of many of these therapies (37,000 dollars with the newer agents versus $391 for the classic six cycles of intravenous CMF), is it possible to achieve equivalent efficacy and yet reduce the economic cost per patient? Only continued clinical trials and cooperative effort among researchers, clinicians, and patients can answer these questions and improve care for breast cancer.

[Role for aromatase inhibitors as adjuvant treatment of breast cancer in menopaused women: facts and questions in 2005]

After a dominant role for more than 30 years, tamoxifen has been progressively replaced by aromatase inhibitors as adjuvant treatment for breast cancer in the menopaused woman. We present here a recall of the mechanisms of action involved together with a review of clinical trials leading to the current situation. Giving trial results in detail, we discuss the current evidence as well as open questions. The populations concerned and trial methodologies are analyzed. Comparative tolerance is detailed. Several questions remain open, either due to the lack of evidence to be obtained from ongoing trials or sufficient follow-up. The evidence presented is commented in light of the American (ASCO) and European (Saint-Gallen) or French (Saint-Paul) guidelines.