Pasadena, CA—Breast cancer patients who use aromatase inhibitors instead of tamoxifen don’t appear to increase their risk of fatal cardiovascular events, although they tend to have more heart problems that are less serious, according to a new study.

The research, published online recently by JAMA Oncology, found no higher incidence of heart attacks and strokes compared to patients using tamoxifen, which has been associated with a serious risk of stroke.

Kaiser Permanente researchers note that women who only used aromatase inhibitors or switched to the drugs after tamoxifen treatment had a 26% to 29% greater risk of less serious cardiovascular events, such as abnormal heart beat and pericarditis, compared with those who only used tamoxifen.

Background information in the article points out that aromatase inhibitors have been found superior to tamoxifen in reducing risk of cancer recurrence in postmenopausal women with hormone receptor positive breast cancer, but that previous studies have provided inconclusive or mixed results on the potential cardiovascular risk associated with the newer drugs.

“Our study is a comprehensive assessment of the impact aromatase inhibitors have on cardiovascular risk and provides reassurance that the hormone therapy to reduce breast cancer recurrence does not increase risk of the most fatal cardiovascular events,” noted lead author Reina Haque, PhD, MPH, a research scientist at Kaiser Permanente’s Southern California Department of Research & Evaluation. “A particular strength of our study is that we accounted for women’s other potential cardiovascular risk factors as well as medication used to treat high blood pressure and high cholesterol.”

Tamoxifen is recommended for 5 years for women with breast cancer to reduce their chances of developing a recurrence. While some postmenopausal women use only aromatase inhibitors, others might use tamoxifen for 1 to 5 years and then begin using aromatase inhibitors, study authors note.

This study included a cohort of 13,273 postmenopausal breast cancer survivors who were diagnosed with a breast cancer, either estrogen or progesterone receptor positive, from 1991 to 2010. The patients, who were followed through 2011 or a maximum of 21 years, were divided into four groups based on the drugs they received:

• 31.7% were treated only with tamoxifen;
• 28.6% only with aromatase inhibitors;
• 20.2% used both; and
• 19.4% did not use any of these drugs.

Results indicate that 3,711 cardiovascular events occurred, but that the aromatase inhibitor-only users had a similar risk of cardiac ischemia—myocardial infarction and angina—with a hazard ratio of 0.97 for both as tamoxifen-only users.
Study authors call for more research on the increased incidence of nonserious cardiovascular events in the patients using the newer drugs.

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