Comparative assessment of lipid effects of endocrine therapy for breast cancer: Implications for cardiovascular disease prevention in postmenopausal women

SummaryCardiovascular disease (CVD) is the leading cause of death in the developed world for both men and women. Women experience significant alterations in lipid profiles during the years following menopause, including a reduction in plasma high-density lipoprotein cholesterol and an elevation of plasma low-density lipoprotein cholesterol, and are at an increased risk of CVD. These changes are due in part to the reduction in estrogen production following the onset of the menopause. Therefore, agents that have anti-estrogenic effects, such as most endocrine therapies for breast cancer, may increase the risk of CVD.Tamoxifen, historically the standard endocrine therapy, has an overall beneficial effect on lipid profiles. However, long-term data from clinical trials have failed to demonstrate a cardioprotective effect and patients treated with tamoxifen did not experience fewer cardiovascular events compared with those receiving placebo. Indeed, a number of studies have shown that tamoxifen may have a detrimental effect, with a significantly increased risk of venous thromboembolic events, pulmonary embolism and stroke.The third-generation aromatase inhibitors (AIs) have demonstrated an improvement in efficacy and tolerability over previous treatments. Since they have a different mechanism of action to tamoxifen, they are not anticipated to exert the same impact on lipid profiles. Clinical trials with anastrozole demonstrated no clinically relevant impact on lipid profiles in postmenopausal patients with advanced breast cancer. However, as lipid profiles are surrogate endpoints, the most appropriate endpoint is the incidence of cardiovascular events in long-term studies. This is of particular relevance in the treatment of early breast cancer, where endocrine agents may be used in the adjuvant setting for periods of 5 years or more. Long-term adjuvant anastrozole treatment resulted in significantly fewer thromboembolic and cerebrovascular events and a similar incidence of ischemic cardiovascular events compared with tamoxifen. The effects of the other AIs on lipid levels are variable, and any correlation with cardiovascular events is currently unknown.