Study: Heavy Antibiotic Use Linked To Breast Cancer

Common antibiotics may make you feel better, but using too many might increase breast cancer risk, according to new research.

In a large study released Monday, researchers at the University of Washington found women who used heavy doses of antibiotics appear to have a greater risk of developing breast cancer.

Researchers were quick to say this doesn't mean that antibiotics cause cancer, and they're calling for a lot more research to even confirm an association. But the idea that medication this common may have a major side effect is raising concern.

The findings are making Joan Dressler, 64, think twice about the antibiotic regimen she's been taking for 30 years.

"Part of me is afraid, and the other part of me wants to hold tight on a positive treatment program," said Dressler, whose family has a history of breast cancer.

In the study, published in Wednesday's issue of the Journal of the American Medical Association, researchers reviewed medical records of more than 10,000 women over eight years. They found that women who took antibiotics for more than 500 days, or had more than 25 prescriptions, had twice the risk of getting breast cancer.

The study involved more than 2,200 women 20 and older who developed invasive breast cancer and almost 8,000 women who did not get breast cancer.

"The more antibiotics a woman used, the higher likelihood she had of developing breast cancer," lead researcher Dr. Christine Velicer said. "However, with that said, it's very important to note that we can't say from this study that antibiotics actually caused the increased breast cancer risk."

That's because other factors could be at play. While antibiotics have been associated with changes in immune function and certain hormones, it could simply be that whatever makes a woman more prone to infections that would require antibiotics, also makes her more prone to breast cancer.

"Women who have an underlying disease which requires them to take antibiotics -- chronic infection, chronic sinuses, that kind of thing -- may have a loss of their immune mechanism. Their immunity may be down. And if your immunity is down, you may be at a higher risk to get breast cancer," said Dr. Thomas Frazier, director of the Breast Cancer Center at Bryn Mawr Hospital in Bryn Mawr, Pa.

Frazier said breast cancer is an immune disease.

"If you don't fight foreign cells bacteria, viruses, etc., well, you're not going to fight a foreign cancer cell well," Frasier said.

"This is not a time to say, 'Oh, all antibiotics are bad'; after all, antibiotics are an extremely useful tool for the treatment of infections," said Dr. John Potter, of Fred Hutchinson Cancer Research Center in Seattle.

The researchers pointed out that the study's findings are another reason to make sure antibiotics are used only when necessary.

"As always, the question is do you really need to be on those antibiotics or not? This is a reminder that if you don't have to be on antibiotics, you probably shouldn't be on antibiotics," said Dr. Hal Burstein, of the Dana Farber Cancer Institute in Boston.

Experts say if you need to be on antibiotics, do so, but make sure to have regular doctor visits, including regular mammograms.

Frazier recommends that women work to improve their immune systems so they don't need so many antibiotics, and that could help them in the fight against breast cancer. He said excercising, eating healthy foods, reducing stress and stopping smoking are all things that can be done to prevent many life-threatening illnesses.

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