Antibiotics and breast cancer


Joel M . Eichen

Overusage of Antibiotics and Breast Cancer (?)

Posted: 2/17/2004 8:20:36 AM

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This report just in ......... A new study has found a possible
connection between the use of antibiotics and breast cancer.



Posted on Tue, Feb. 17, 2004

Breast cancer may have link to antibiotics

By Marie McCullough

Inquirer Staff Writer

A new study has found a possible connection between the use of antibiotics and breast cancer.

Seattle researchers analyzed pharmacy records of more than 10,000 women in a health plan and found
that those diagnosed with breast cancer in the previous eight years were twice as likely as women
without breast cancer to have been high users of antibiotics.

Because antibiotics are widely used and breast cancer is the most common malignancy in women
worldwide, the findings, published in this week's Journal of the American Medical Association,
immediately triggered anxiety among women and their doctors.

But the researchers and other experts cautioned that this type of study, which looks backward for
key differences between groups, has many limitations. It cannot say whether antibiotics cause breast
cancer or, if so, how much an individual's risk of breast cancer would increase.

"This is not a finding on which to make medical or policy decisions," said John D. Potter, an author
of the study and an epidemiologist at Fred Hutchinson Cancer Institute in Seattle. "The next step is
to test whether it's an important association."

High antibiotic use, which was also associated with death from breast cancer, was defined as more
than 500 days, or more than 25 prescriptions within the previous 17 years. Less antibiotic use was
also correlated with increased breast-cancer risk, although the association was small.

The link was seen regardless of the class of antibiotics or the diagnoses, which included acne,
respiratory infections and bladder infections.

On average, a woman has a 1-in-8 chance of developing breast cancer over her lifetime. Each year in
the United States, more than 280,000 cases of breast cancer are diagnosed, and about 40,000 women
die of the disease.

"None of us believe you can conclude breast cancer is caused by antibiotics at this point," said
family physician Stephen H. Taplin, a coauthor of the study who is now at the National Cancer
Institute. "There is an association... but it's not huge. It is something to look at more

'Intriguing, but...'

In an editorial in the journal, Jane A. Cauley, a University of Pittsburgh professor of
epidemiology, said the findings were "potentially worrisome" but raised many questions.

"It's intriguing, but I don't think it should change clinical practice," she said in an interview.

More than 70 percent of women in the new study had from one to 25 antibiotic prescriptions over the
previous 17 years. Eighteen percent of the women without cancer had not filled any antibiotic
prescriptions, compared with 15 percent of those with it. Nine percent of women without cancer and
12 percent of women with the disease fell into the high-use category.

In 1981, scientists first proposed that antibiotics may increase breast-cancer risk, but the only
other study to examine the question was in Finland in 2000. That study also found an association,
but it was not as well-designed.

The Seattle researchers offer several possible biological explanations for antibiotics' role in
cancer. The drugs may disrupt microbes that live in the intestines, or may trigger immune responses
or inflammation.

Underlying problem?

On the other hand, the authors say, the need for antibiotics may be a sign of a broader, underlying
problem. Perhaps women with weakened immune systems, for example, are more susceptible to cancer as
well as infections.

It is also possible that the apparent link between antibiotics and breast cancer happened because
the researchers, who could not perfectly match the two groups of women, accidentally skewed the
results. For example, the women who were diagnosed with breast cancer had more risk factors -
including younger age at first menstruation, later age at first childbirth, and more family history
of breast cancer - than the women without cancer. The women with cancer also had higher rates of

Although the researchers tried to make statistical adjustments for such differences, the study may
have been "confounded by unmeasured factors," Cauley said.

In any case, experts agreed, the study adds to the list of reasons to use antibiotics carefully and
sparingly. Overuse and unnecessary use of antibiotics have caused many infectious organisms to
become resistant to treatment.

"The big problem in the U.S. is people taking antibiotics without good cause," Taplin said.

Contact staff writer Marie McCullough at 215-854-2720 or [email protected] This story
includes information from the Washington Post.

Joel M. Eichen, . Philadelphia PA



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