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Updated: 2004-02-16 16:07:34 -0400 (Reuters Health)
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. 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.
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.
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.
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.
"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.
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.
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."
"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."
The study provides more questions than answers, they add.
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.
SOURCE: Journal of the American Medical Association, February
18, 2004.
