Type of Breast Cancer Drug May Raise Risk of Heart Disease

Breast cancer patients who take drugs called aromatase inhibitors after surgery face an increased risk of developing heart disease, according to new research.

The risk of having a heart attack, heart failure or other major cardiovascular disease was 20 percent greater among women taking an aromatase inhibitor (AI) than those taking another drug called tamoxifen, an analysis of 29,000 breast cancer patients has found. Both tamoxifen and AIs are used to treat women whose breast cancer is fed by the hormone estrogen.

Earlier work had suggested a link between AIs and heart disease, but the new study included data from more patients and a longer follow-up period, said researcher Dr. Eitan Amir, an oncologist at Princess Margaret Hospital in Toronto. Longer follow-ups are necessary to study side effects such as heart disease, which can build slowly and take a long time to become apparent.

"Clinicians who treat breast cancer with AIs see the rise in cholesterol quite often. The expectation was that if people have high levels for long enough, this will happen," Amir said.

The study may add fuel to the ongoing debate about whether AIs or tamoxifen are better for patients in the long run.

"Most clinicians have firm views, and it's a contentious area," Amir said.

Each drug comes with its own set of side effects, he said, and his study revealed that patients who switch from one drug to another may be better off than those who remain on a single drug over the course of their treatment. The toxic effects of drugs can accumulate slowly; switching treatments could allow women to avoid reaching the level where side effects could affect their health.

Tamoxifen has been used for more than 30 years, and works by blocking estrogen's effect on breast cancer cells. However, it brings an increased risk of developing endometrial cancer (which begins in the lining of the uterus) or blood clots that can lead to stroke.

AIs have been approved for nearly a decade (there are three available) and work by blocking the body's production of estrogen. Amir said a trend among patients taking AIs has become clear: They are less likely than patients taking tamoxifen to see their breast cancer recur after treatment. However, they are not likely to live any longer than patients taking tamoxifen.

The new study provides evidence of why this seeming discrepancy exists, Amir told MyHealthNewsDaily. Because the cardiovascular side effects of AIs can be deadly, patients may die from them before their breast cancer returns. Since 2008, the Food and Drug Administration has required that one of the AIs, anastrozole, carry a label warning of the potential for these effects.

In Amir's study, he and his colleagues conducted a meta-analysis of all seven of the large clinical trials that have compared tamoxifen and AIs, involving more than 29,000 breast cancer patients. The longest of these trials has been ongoing for eight years. The last such meta-analysis was conducted three years ago and included only four trials, he said, but it was what prompted the FDA to do its own analysis, and led to the labeling requirement.

"The fewest deaths, without breast cancer recurrence," were seen in patients who took tamoxifen for two or three years after their surgery, then switched to an AI for the rest of their treatment, he said. Typically, women remain on drug treatment for five years after surgery.

This switching of treatments, Amir said, "is the only setting in which AIs are shown to have an overall survival benefit."

To be sure, patients' risks for developing certain side effects are affected by other health factors, and physicians should consider such "baseline factors" when selecting a drug, he said.

But in the debate over whether tamoxifen or AIs are better for patients, Amir said, "the best strategy may be a little bit of both."

Pass it on: Aromatase inhibitors may pose serious risks to heart health.

Follow MyHealthNewsDaily Managing Editor Karen Rowan on Twitter @karenjrowan

This article was provided by MyHealthNewsDaily, a sister site to LiveScience.

Karen Rowan
Health Editor
Karen came to LiveScience in 2010, after writing for Discover and Popular Mechanics magazines, and working as a correspondent for the Journal of the National Cancer Institute. She holds an M.S. degree in science and medical journalism from Boston University, as well as an M.S. in cellular biology from Northeastern Illinois University. Prior to becoming a journalist, Karen taught science at Adlai E. Stevenson High School, in Lincolnshire, Ill. for eight years.