Women who take tamoxifen for breast cancer may be getting a benefit from the drug that goes beyond its cancer-fighting properties. Researchers from Boston University found that the drug may also lower the risk of heart attack and angina, a type of chest pain that is a common symptom of heart disease.

They compared more than 3,000 breast cancer patients treated with tamoxifen to more than 4,000 women with other cancers (bladder, colon, or non-melanoma skin cancer) who did not receive tamoxifen. The women on tamoxifen had a significantly lower rate of heart attacks and cases of angina, even when their age was taken into consideration.

"The real crux of the finding is that we have found a 50% reduction in risk, and when we look at it in different ways and compare it with the other cancers, the effect is still there," said study coauthor Susan Jick, DSc, MPH, an associate professor of epidemiology at Boston University School of Public Health and co-director of the Boston Collaborative Drug Surveillance Program.

"For someone who's got cancer and is being treated, that's important and hopeful knowledge," she said.

The findings were published in the Feb. 14 online edition of the journal Cancer and will appear in the March 15 print edition (Vol. 103, No. 6).

The results weren't entirely surprising. Other studies have shown that tamoxifen can reduce levels of cholesterol, homocysteine, and other substances that raise the risk of heart disease. But those results haven't always been consistent.

Jick's study is important because she and her colleagues had particularly good information about how long the women had been taking tamoxifen and how much of the drug they had taken -- information gathered from medical records, not from women's recollections. Another strength: The women used for comparison were also cancer patients.

"We used other women with cancer, so everyone is under close medical attention and seeing a doctor regularly, so if this person developed heart disease she would be equally likely to be diagnosed," Jick said.

While this may be good news for women taking tamoxifen to prevent or treat breast cancer, it doesn’t mean that women should start taking the drug solely to prevent heart disease. Tamoxifen can have side effects. For example, women who take it are known to be at higher risk for blood clots and certain gynecologic cancers.

Furthermore, Jick said more studies are needed to confirm her results and get a better understanding of just how tamoxifen works against heart disease.

For instance, the heart-friendly effects seemed to begin within two years of starting tamoxifen treatment -- but the researchers aren't sure how long those benefits might last. Women who had used tamoxifen in the past also showed a lower risk of heart disease, but the effect wasn't as strong and there were fewer past users than current users in the study.

"Whenever you find some protective effect you want to know what it is about this treatment that's protecting, and what can we learn about that for additional therapy for non-cancer patients and for the general population," Jick said.