DNC NEWS:  Antibiotics and Breast Cancer Risk

Subject:  A study published in JAMA suggests that antibiotic use increases the risk for breast cancer.

A study published in the February 17, 2004 edition of the Journal of the American Medical Association (JAMA) found a strong link between antibiotic use and breast cancer.    This made the front page in most papers, so it probably isn't news to most of you.  I'll paste a summary article or two below.  JAMA is allowing a free download of the entire article if you are interested at:
( http://jama.ama-assn.org/cgi/content/full/291/7/827 )

This week's NIH Newsletter summarizes the study as follows:
"The authors of this JAMA study found that women who took antibiotics for more than 500 days - or had more than 25 prescriptions -over an average period of 17 years had more than twice the risk of breast cancer as women who had not taken any antibiotics. The risk was smaller for women who took antibiotics for fewer days. However, even women who had between one and 25 prescriptions over an average period of 17 years had an increased risk; they were about 1.5 times more likely to be diagnosed with breast cancer than women who didn't take any antibiotics. The authors found an increased risk in all classes of antibiotics that they studied."

This of course is distressing news.  The big question is whether the antibiotics cause the increased risk or are women who need more antibiotics also more prone to getting cancer.  Data from the study are unable to answer this question.  But stay tuned, a great many researchers are asking themselves the same question this Sunday morning.

If antibiotic usage does increase breast cancer risk, the question will be why.  We can toy with various explanations. The most obvious is the disruption in normal gut flora caused by antibiotics.  The normally huge population of bacteria in the intestines is essential for healthy immune function; disrupting them may lower immune function increasing risk for cancer.  These bacteria also protect the body by inactivating certain carcinogens.  Although germs are supposed to be more susceptible to injury from antibiotics than your body's cells, this doesn't mean antibiotics have no effect on healthy cells.  The mitochondria, the organelles within each cell responsible for generating energy, are very similar to bacteria and may be sensitive to antibiotics. 

Here is a story about this from the Guardian:

 
Breast cancer risk linked to antibiotics

James Meikle, health correspondent
Wednesday February 18, 2004
The Guardian

Women who use antibiotics to treat infections may be increasing their risk of breast cancer, a US study has suggested.

Researchers found that women who used the drugs for up to 500 days were about 1.5 times as likely to develop cancer. Among higher users, the risk of death from the disease was nearly 3.5 times as great.

The association between disease and death was even stronger among those who used antibiotics for longer, although the authors of a report in the Journal of the American Medical Association stressed that more research was needed to establish whether the apparent association was causal or if other factors needed to be considered.

These included the possibility that immune systems were already undermined by conditions for which antibiotics were being taken or that inflammation of tissues linked to some conditions made them more suitable breeding grounds for tumours.

Scientists are already concerned about the excessive use of antibiotics to treat infections, blaming it for growing bacterial resistance to drugs.

The study, led by Christine Velicer of Washington University, Seattle, compared medical data for 2,266 women who had breast cancer with 7,953 women who did not.

In the report on their work, the researchers said: "While the implications for clinical practice will not be clear until additional studies are conducted, the results of this study support the continued need for prudent long-term use of antibiotics."

Peter Sasieni, of Cancer Research UK's department of epidemiology, mathematics and statistics, emphasised that there was no proof of a causal link nor any plausible biological explanation for how the drugs might cause cancer.

The hypothesis deserved to be studied further, Professor Sasieni said, but, "in the meantime, the proven value of antibiotics for bacterial infections certainly outweighs the possible future increased risk of breast cancer".


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