FRIDAY, Dec. 9, 2005 (HealthDay News) -- A huge study involving more than 500,000 women suggests that breast cancer survivors are 25 percent more likely to develop cancer in another part of their body than women without a history of the disease.
It's not entirely clear why this extra risk exists. According to researchers, it may have something to do with genetics, environmental factors, or the destructive effects of chemotherapy and radiation treatments.
Regardless of the cause, breast cancer survivors should keep the findings in perspective, said Debbie Saslow, director of breast and gynecologic cancer with the American Cancer Society. While the risk of a second cancer does seem to be higher in breast cancer survivors, the actual number of extra cases is small.
"Women should not panic," she said.
Previous research has suggested that breast cancer survivors have a 20 percent to 30 percent higher risk of developing a second cancer in another part of the body. The new study aimed to look at a large population of women, 525,527 patients with a history of breast cancer. The women's medical histories from 1943 to 2000 were recorded in national cancer registries in Europe, Canada, Australia and Singapore.
The findings appear in the Dec. 8 online issue of the International Journal of Cancer.
Breast cancer survivors were especially prone to develop cancer in the connective tissue of the thorax and the arms. Their rates of those cancers were almost six times as high as other women; the researchers suspect that radiation therapy could have harmed those areas around the breast.
Chemotherapy may also play a role in raising the risk of endometrial cancer, which affects the lining of the uterus. According to the study authors, the breast cancer drug tamoxifen has long been blamed for increased cases of endometrial cancer, but the researchers found a raised risk even before the drug was commonly used.
So is breast cancer treatment potentially dangerous to the future health of a patient?
Yes, said study author Lene Mellemkjaer, a senior researcher at the Danish Cancer Society's Institute of Cancer Epidemiology. But she added that "It is important to emphasize that even though the treatment for breast cancer has side effects in terms of increasing the risk of other types of cancer, the treatment is crucial for survival after breast cancer."
Some increased risks, in fact, may have nothing to do with breast cancer treatment. Obesity seems to contribute both to breast cancer after menopause and future cases of colorectal and kidney cancer, while genetic predispositions seem to raise the risk of both breast cancer and later cases of ovarian cancer.
Overall, the researchers estimated that the increased risk will lead to an extra 16-17 cases of cancer per year among every 10,000 women with breast cancer.
What to do? According to Saslow, doctors are already taking action to reduce the risk of cancer treatments.
"For example, radiation therapy is targeted better to the cancer site, and the nearby organs are better protected," she said. Meanwhile, she said, the risk of endometrial cancer should drop as other drugs replace tamoxifen.
Future research, meanwhile, should look more deeply at the risk of second cancer to figure out exactly what's going on, Mellemkjaer said. Also, future research could help doctors pinpoint which individual patients are at highest risk.
In a related study, researchers at Duke University Medical Center report that low levels of two ovarian hormones, called inhibin A and B, predict which patients might become infertile after breast cancer chemotherapy.
"Identifying hormones that predict the likelihood of ovarian failure will enable us to take steps to prevent such damage before cancer treatments begin," lead researcher Dr. Cary Anders said in a prepared statement.
The findings were to be presented Thursday at the annual San Antonio Breast Cancer Symposium.
More information
Learn more about breast cancer from the Susan G. Komen Breast Cancer Foundation.
