Aromatase inhibitors—hormonal therapy drugs commonly used in the treatment of postmenopausal breast cancer—may increase the risk of heart disease. These results were presented at the 2010 San Antonio Breast Cancer Symposium.
Tamoxifen and aromatase inhibitors are hormonal therapy drugs that are commonly used in the treatment of hormone receptor-positive breast cancer. Both types of drugs slow or stop breast cancer growth by reducing the effects of estrogen on the breast.
Aromatase inhibitors include Arimidex® (anastrozole), Femara® (letrozole), and Aromasin® (exemestane). In studies that compared aromatase inhibitors to tamoxifen in postmenopausal women, aromatase inhibitors tended to be more effective against breast cancer recurrence. As a result, treatment guidelines recommend that postmenopausal women with hormone receptor-positive breast cancer consider using an aromatase inhibitor at some point in their course of treatment.
Adverse effects of tamoxifen and aromatase inhibitors differ. Blood clots and endometrial (uterine) cancer are more common with tamoxifen, and bone loss is more common with aromatase inhibitors. Previous studies have also raised questions about the effects of aromatase inhibitors on the heart.
To further evaluate the issue of heart problems, researchers collected information from seven large clinical trials that compared tamoxifen with an aromatase inhibitor among postmenopausal breast cancer patients.
Compared with tamoxifen, use of an aromatase inhibitor was linked with a 26% increase in risk of heart disease. This is not a large increase in risk, but the researchers speculated that the risk may be greater for women who have other risk factors for heart disease. In a second study conducted using data from health insurance plans, there did not appear to be an increased risk of cardiac disease among women taking aromatase inhibitors.
Unfortunately, it is not possible to determine at this time if aromatase inhibitors truly increase the risk of heart problems. Women are encouraged to discuss potential risks and benefits of all treatments with their physicians.
 Burstein HJ, Prestrud AA, Seidenfeld J et al. American Society of Clinical Oncology Clinical Practice Guidelines: Update on adjuvant endocrine therapy for women with hormone receptor-positive breast cancer. Journal of Clinical Oncology. 2010; 28: 3784-3796.
 Amir E, Ocana A, Niraula S, Carlsson L, Seruga B. Toxicity of adjuvant endocrine therapy in postmenopausal breast cancer patients. Presented at the 33rd annual San Antonio Breast Cancer Symposium, December 8-12, 2010. Abstract S2-7.