New generation aromatase inhibitors in breast cancer. Weighing out potential costs and benefits

Economic evaluation of aromatase inhibitors for the treatment of breast cancer

Breast cancer affects 1 million women a year. Hormonal therapy has been a mainstay of treatment for women with hormone-sensitive breast cancer. The newer class of aromatase inhibitors has challenged the use of the previous standard agent, tamoxifen, in the treatment and prevention of breast cancer. This article will provide a thorough review of the literature on the newer generation aromatase inhibitors and examine their role in metastatic, adjuvant, neoadjuvant and prevention settings. An in-depth review of the cost-efficiency analyses is also performed. Recent studies on the newer, third-generation aromatase inhibitors have challenged the previous gold standard (tamoxifen) in the prevention and management of hormone-sensitive breast cancer in postmenopausal women. These studies have supported the use of aromatase inhibitors as first-line therapy in both early (adjuvant) and advanced breast cancer management. Whether aromatase inhibitors should replace tamoxifen in these settings is still a matter of debate. Augmenting these studies and providing additional information to the debate are pharmacoeconomic appraisals, which help to place a societal value on newer therapies as compared with the previously established therapy. This review discusses the pharmacology and efficacy of the newer aromatase inhibitors as it applies to their role in the metastatic, adjuvant, neoadjuvant and prevention settings. The pharmacoeconomic studies performed on these agents are also discussed.

The role of aromatase inhibitors in early breast cancer

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 receptor-positive 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.