- NEW YORK (Reuters
Health) -- The use of antibiotics appears to be associated with an increased
risk of breast cancer and fatal breast cancer, according to the results
of a new study reported in this week's issue of the Journal of the American
Medical Association.
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- However, the investigators add that although a relationship
has been found, their findings do not prove that antibiotic use is the
cause of breast cancer in these women and they note that other factors
may be involved.
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- Earlier reports have suggested a link between antibiotics
and increased cancer risk, lead author Dr. Christine M. Velicer of the
University of Washington, Seattle and colleagues note.
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- The effects of these drugs on the microorganisms normally
found in the intestines and the way estrogen is processed, as well as their
effects on the immune system and on inflammation, have been suggested as
possible ways antibiotics may influence the development of cancer.
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- To further investigate a possible relationship, Velicer's
group evaluated data collected for 2266 women with primary, invasive breast
cancer between 1993 and 2001, and 7953 randomly selected women without
breast cancer who were enrolled in the same health plan.
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- "We found that increasing cumulative days of antibiotic
use and increasing cumulative number of antibiotic prescriptions were associated
with increased risk of incident breast cancer, after controlling for age
and length of enrollment," they report.
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- When compared with women with no history of antibiotic
use, women with cumulative antibiotic use for 1 to 500 days had a 2.5-fold
increase risk of breast cancer. "Increasing cumulative days of antibiotic
use was also associated with death due to breast cancer, controlling for
age, length of enrollment, and ever use of postmenopausal hormones,"
they write.
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- The investigators stress, however, that "it cannot
be determined from this study whether antibiotic use is causally related
to breast cancer, or whether indication for use, overall weakened immune
function, or other factors are pertinent underlying exposures."
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- "This observation is potentially worrisome in that
antibiotic exposure is common and sometimes nonessential," Drs. Roberta
B. Ness and Jane A. Cauley of the University of Pittsburgh comment in an
accompanying editorial. "Thus, if real, the risk of breast cancer
attributable to the use of antibiotics could be large and partially preventable."
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- The study provides more questions than answers, they
add.
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- Both the authors and editorialists agree that the clinical
implications of the study are unclear and than more studies are needed
to explore the relationship between antibiotic use and cancer risk.
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- SOURCE: Journal of the American Medical Association,
February 18, 2004.
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