Antibiotics linked with increased breast cancer risk
Long-term use of antibiotics is associated with an increased risk of breast cancer, US researchers report. Their study, published this week
in JAMA, does not indicate whether the link is causal but the researchers
warn that the findings support the need for prudent long-term use of
these drugs (2004;291:827).
Christine Velicer, of the department of epidemiology, University of Washington,
Seattle, and colleagues conducted a case-control study in which they
compared antibiotic use among 2,266 women with invasive breast cancer
and 7,953 randomly selected controls.
They found that increasing cumulative days of antibiotic use were associated
with increased risk of developing breast cancer and also of death due
to breast cancer. For women who used antibiotics cumulatively for between
one and 500 days, the risk of developing breast cancer was at least 1.4
times that for women who had not used antibiotics. Risk rose with increased
cumulative use and all classes of antibiotics studied were associated
with increased risk.
The researchers also looked at a subset of women who used macrolide and
tetracycline antibiotics for either acne or respiratory tract infections.
They reasoned that because the severity of acne can be related to levels
of oestrogen, this indication for antibiotic use might be associated
with an increased risk of breast cancer. However, risk of developing
the disease was similar for both indications.
The researchers say the hypothesis that some classes of antibiotics may
increase risk of breast cancer is plausible. For example,
certain antibiotics may reduce the capacity of intestinal microflora
to metabolise phytochemicals that protect against carcinogenesis. In
addition, tetracyclines, through stimulation of prostaglandin E2, are
implicated in cyclo-oxygenase 2 overexpression, which is associated with
mammary carcinogenesis.
“Although this evidence suggests that antibiotics may be associated
with breast cancer, it is also possible that a weakened immune system
is the
biologically relevant basis of this association,” they add.
The authors of an accompanying editorial (ibid, p880) say the study results
are potentially worrying because antibiotic exposure is common and sometimes
non-essential. “If real, the risk of breast cancer attributable
to the use of antibiotics could be large and partially preventable,” they
say.
However, they also point out that confounding factors may have contributed
to the observed association. |
The
Pharmaceutical Journal