Aromatase Inhibitors May Raise Heart Risks

Newer Breast Cancer Drugs May Carry Higher Risk of Heart Problems Than Tamoxifen: Study

By Charlene Laino
WebMD Health News

Reviewed By Laura J. Martin, MD

Dec. 9, 2010 (San Antonio) -- Postmenopausal women with early breast cancer who take newer hormone drugs known as aromatase inhibitors are 26% more likely to develop heart disease than those who take the old standby tamoxifen, researchers report.

"Treatment with aromatase inhibitors is associated with a significant increase in the risk of cardiovascular events, specifically heart attacks, angina, and heart failure , compared with tamoxifen," says Eitan Amir, MD, a senior fellow in oncology and hematology at the Princess Margaret Hospital in Toronto.

However, the actual risk of any individual woman developing heart problems was relatively small -- about 4% -- in women taking either aromatase inhibitors or tamoxifen, he says.

In fact, the analysis showed that 132 patients must be treated with an aromatase inhibitor before one cardiovascular problem occurs. "This number needed to harm is relatively high," Amir says.

But a woman who already has risk factors for heart disease and takes an aromatase inhibitor has a 7% chance of developing heart problems, Amir tells WebMD.

For the study, Amir polled the results of seven trials of tamoxifen and aromatase inhibitors involving nearly 30,000 postmenopausal women with early breast cancer.

The study was presented at the San Antonio Breast Cancer Symposium.

Aromatase Inhibitors vs. Tamoxifen: How they Work

About two-thirds of breast tumors are fueled by estrogen.

Tamoxifen, which blocks estrogen from getting into cancer cells, slowing tumor growth, has been used for decades to treat breast cancer.

In recent years, its use has been largely supplanted by aromatase inhibitors, which actually shut down the body's ability to make estrogen.

Aromatase Inhibitors vs. Tamoxifen: What Should Women Do?

The findings suggest that women at risk for heart disease should limit use of aromatase inhibitors, Amir says.

"Starting with tamoxifen and then switching to an aromatase inhibitor after several years -- rather than starting with an aromatase inhibitor and staying on it -- may reduce the risk of dying from causes other than breast cancer," he says. "But this is just a hypothesis at this point."

An expert who worked on the landmark ATAC study that first showed the effectiveness of aromatase inhibitors disagrees.

"The bottom line is that aromatase inhibitors keep postmenopausal women alive and free of disease compared to tamoxifen," says Aman Buzdar, MD, of the University of Texas M.D. Anderson Cancer Center in Houston.

In the ATAC study, women were given either the aromatase inhibitor Arimidex, tamoxifen, or both. "They have now been followed for 10 years and the groups have the same risk of cardiovascular disease," Buzdar tells WebMD.

But other studies have shown a small increased risk of heart problems in women taking aromatase inhibitors, Amir says. Other aromatase inhibitors are Aromasin and Femara.

And in December 2008, the FDA added a warning label to Arimidex cautioning of the increased risk for heart disease, he says.

Aromatase Inhibitors vs. Tamoxifen: Other Findings

Among other findings of the new study:

Women who took aromatase inhibitors were 47% more likely to suffer a fracture than those on tamoxifen, regardless of how long they took the medicine.

Women on tamoxifen were more likely to develop endometrial cancer and dangerous blood clots in the legs.

There was a suggestion that women who switched to aromatase inhibitors after starting on tamoxifen were less likely to die from something other than breast cancer compared with those who started treatment with the newer medications.

The risk of serious side effects was similar when aromatase inhibitors were used as an initial treatment compared with switching to aromatase inhibitors after treatment with tamoxifen.

The much higher cost of the aromatase inhibitors has been an issue for some women. But that is starting to change as generic version of the drugs become available, Buzdar says.

A woman should discuss all the pros and cons of each treatment with their doctor, Amir says.

This study was presented at a medical conference. The findings should be considered preliminary as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.


A lump in the breast is almost always cancer. See Answer

San Antonio Breast Cancer Symposium, San Antonio, Dec. 8-12, 2010.

Eitan Amir, MD, senior fellow, oncology and hematology, Princess Margaret Hospital, Toronto.

Aman Buzdar, MD, department of breast medical oncology, University of Texas M.D. Anderson Cancer Center, Houston.

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