July 7, 2003 Breast cancer survivors appear to be one-third less likely to have a heart attack than other women report researchers from the University of Chicago in the July, 2003, issue of Cancer.
This reduction was most apparent in women with risk factors for heart disease, the leading cause of death in older women.
The researchers suspect that higher natural levels of estrogen, which can increase breast cancer risk, combined with the anti-cancer drug tamoxifen that many breast cancer survivors take to decrease their risk of recurrence, may explain the reduced heart attack rate.
"We found a silver lining around the cloud of a breast cancer diagnosis," said Elizabeth Lamont, M.D., assistant professor of medicine at the University of Chicago and director of the study. "Women with breast cancer have received plenty of bad news," she said. "Now we can give survivors some good news."
The study -- using data from the National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER) study -- compared 5,980 women aged 67 or older who had survived postmenopausal early-stage breast cancer to a group of 23,165 women who had never had cancer. The researchers followed the women for five years.
They found that breast cancer survivors were 34 percent less likely to be hospitalized for heart attacks than women who had not had breast cancer.
The protective effect was slight, less than 15 percent, in women at low risk for heart disease, but it increased to 50 percent or more for women with one or more cardiac risk factors. So, the greater the risk of heart disease, the greater the protection associated with breast cancer.
These results "question the stark dichotomies of 'health' and 'disease,'" say the authors. In this case, one serious disease appears to protect patients from another serious and more common disease.
How breast cancer might prevent heart disease remains unclear. The primary suspect is female hormone levels. Women exposed over a lifetime to higher-than-average levels of estrogen have an increased risk of breast cancer. At the same time, estrogen has been thought to protect women from heart disease.
However, the protective role of supplementary estrogen remains, at best, unclear. The Nurses' Health Study reported in 1996 that women who took estrogen plus progestin beginning at the menopause had 30 percent fewer heart attacks. But last year, the Women's Health Initiative showed that five years of hormone use beginning at menopause was associated with a 29-percent increase in heart disease. Another randomized trial, the Heart and Estrogen/Progestin Replacement Study, concluded that estrogen combined with progestin had no beneficial effects on the heart in women with a history of heart disease.
Drugs, such as tamoxifen, that modulate the effects of estrogen, are often given to women who had had breast cancer. These drugs are also thought to protect the heart. Again, however, studies have not confirmed this effect.
"Although we don't yet know the mechanism, we are encouraged to find a subset of women who have one-third less of the disease that causes the most deaths of elderly women in the United States," said Lamont.
"It's nice to have some good news for women who have breast cancer," added Lamont, who treats cancer patients. "They are less likely to face a heart attack. Now we need to study such patients further to uncover the mechanism behind the risk reduction."
"If we find that drugs like tamoxifen are important in decreasing rates of heart attacks among those patients at high risk, then that suggests tamoxifen might be a good treatment for all women, a "replacement" for hormone replacement therapy."
Co-authors of the paper were Diane Lauderdale, Ph.D., of the University of Chicago, and Nicholas Christakis, M.D., Ph.D., M.P.H, formerly of Chicago and now at Harvard University. The study was supported by grants from the National Institutes of Health.
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