Breast cancer link to use of antibiotics
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Posted on Tue, Feb. 17, 2004
Breast cancer linked to use of antibiotics
NO CAUSE FOUND IN STUDY, BUT THE DRUGS RAISED RISK
By April Lynch
Antibiotic use in women is associated with an increased risk of breast cancer, according to a study released Monday that raises new questions about the underlying causes of the deadly disease.
The study, published in the Journal of the American Medical Association, does not show that antibiotics cause breast cancer.
Researchers behind the study stressed that it is not clear whether antibiotic use might give rise to breast cancer or simply reflect broad health problems, such as persistent inflammation, that might encourage the growth of malignant breast cancer.
But the research is likely to be important for women and their doctors on two fronts. The findings will spur new inquiries into the causes of breast cancer, said scientists not connected with the study. And the findings reinforce the need to make sure infection-fighting antibiotic drugs are prescribed and taken carefully.
``This is not the time to say all antibiotics are bad,'' said Dr. John Potter, a study co-author affiliated with the Seattle-based Fred Hutchinson Cancer Research Center. ``Antibiotics are an extremely useful tool for the treatment of infection, but they must be used appropriately.''
The study, based on health data from more than 10,000 women in the Pacific Northwest, found that women who used the most antibiotics had twice the risk of breast cancer when compared with women who had not been given the drugs. That risk increased as the amount of antibiotics prescribed to a woman went up.
The study was led by researchers at Group Health Cooperative, a Seattle-based health care provider that sees patients in Washington and Idaho. Researchers started with health data from more than 2,200 women cared for by Group Health Cooperative who had been diagnosed with invasive breast cancer between 1993 and 2001.
They then compared the medical histories of the breast cancer patients with those of about 7,900 female patients who did not develop breast cancer, looking at everything from age to weight to the amount of antibiotics the women had been prescribed, over an average of 17 years.
The more antibiotics the women had been prescribed, the higher the risk of breast cancer, they found. Women who had been prescribed smaller amounts of antibiotics -- anywhere from one to 25 prescriptions -- were about 1 1/2 times more likely to get breast cancer than those who took no antibiotics. Women who had received more than 25 prescriptions had twice the risk of breast cancer.
This increased risk stayed constant regardless of the type of antibiotic the women had taken or the specific ailment the drugs had been prescribed for, the researchers said.
The study expands on results from a less comprehensive investigation conducted in Finland and published in 2000 that found women who had taken antibiotics for bladder infections had an increased risk of breast cancer. Now, other scientists said, research will likely focus on why antibiotics and breast cancer appear to be connected.
``The study talks about an association, but it's very clear that it's not showing cause and effect,'' said Rebecca Garcia, vice president of health sciences for the Susan G. Komen Breast Cancer Foundation, a group that drives research and patient support efforts. ``We still don't have a lot of answers right now as to what causes breast cancer.''
Breast cancer strikes more than a million women worldwide each year, and is the second-leading cause of cancer deaths in U.S. women.
Focus on infection
Scientists and doctors behind and outside the study pointed to health problems such as infection or inflammation as an especially promising area of focus. Inflammation, a frequent result of infection, has already been linked to some other types of cancers. Infection is also the medical reason for prescribing antibiotics. Hence, antibiotics might be associated with breast cancer not because they cause the disease, but because they accompany other health problems that could give rise to cancer.
The study findings showing that many types of antibiotics were all linked with an increased risk for breast cancer has some doctors especially curious about the inflammation question. Different types of antibiotics work differently in the body, and some doctors said it is questionable whether such different drugs could somehow all wind up causing the same illness.
``They see the same level of risk for different antibiotic classes, which makes me think that what they're measuring is not antibiotics but something else,'' said Dr. Robert Carlson, a breast cancer specialist and professor of medicine at Stanford University. ``Women who take antibiotics on a frequent basis are often different from women who don't.''
Some of those differences often lie in long-term medical problems. Women who take antibiotics frequently may get recurring bladder infections or suffer from chronic skin or upper respiratory infections. Sometimes, they may be in poorer overall health.
Such concerns are what drive one Mountain View woman to pay close attention to her own health -- and limit her use of antibiotics. Sylvia Coluzzi, 62, hasn't taken the drugs in about five years. She watches stress, fatigue and her diet to keep herself well, and doesn't ask her doctor for unnecessary antibiotics. She has no history of breast cancer.
``I just went through that horrible flu everyone had in December, and I think I may have had a sinus infection,'' Coluzzi said. ``But the flu is a virus, and I didn't want to take antibiotics for it. It was really about sleep, and lots of chicken soup, and then I got better.''
Such care in using antibiotics is what researchers behind the breast cancer study recommend while more research goes forward. With so many unanswered questions about breast cancer, women shouldn't reject antibiotics, but they also shouldn't misuse them, doctors said.
``When you are trying to save a life, and antibiotics will help you do that, considerations about breast cancer risk should not enter the equation,'' said Stanford's Carlson. But, he said, this study ``should caution patients about going to the doctor and insisting on antibiotics for colds and the flu and other things that aren't helped by antibiotics.''