Antibiotics may boost breast cancer risk

Fungi can affect the ducts.

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Thursday Dec 12, 2013 (foodconsumer.org) -- Breast Cancer risk may be increased in women who use Antibiotics , a study in JAMA suggests.  The more antibiotics they use, the higher risk they will have to face.

The case-control study led by researchers at Fred Hutchinson Cancer Research Center in Seattle and Applied Research Program, National Cancer Institute in Bethesda, Maryland shows that those who used antibiotics for more than 1000 days doubled their risk for developing breast cancer.

The study leads to a suggestion.  More research is needed to prove or disprove that the association between use of antibiotics and Breast Cancer risk is a work of chance or a causal relation.

However, the authors conducted the study because they believed that it is possible that use of antibiotics can potentially promote the development of Breast Cancer because they know that antibiotics have an effect on immune function, inflammation and metabolism of estrogen and phytochemicals, all of which are associated with risk of breast cancer.

For the study, researchers identified 2266 women older than 19 years who were diagnosed with primary invasive breast cancer through a health plan for at least one year and 7953 controls randomly selected from those who also enrolled in the plan.  Cases were ascertained from the Surveillance, Epidemiology, and End Results cancer registry and Antibiotic use was ascertained from pharmacy records.

The researchers found increasing cumulative days of Antibiotic use were correlated with elevated risk of incident breast cancer after adjustment for age and length of enrollment.

Specifically, compared with those who never used antibiotics, those who used antibiotics for 1 to 50, 51 to 100, 101 to 500, 501 to 1000 and more than 1000 days were 45%, 53%, 68%, 114% and 107% more likely to be diagnosed with primary invasive breast cancer.

Increased risk for developing breast cancer was found associated with all types of antibiotics.  And increased risk of death was also associated with use of all sorts of antibiotics.

Among women with the highest levels of tetracycline or macrolide use, risk of breast cancer was not elevated in those using these antibiotics exclusively for Acne or rosacea (indications that could be risk factors for breast cancer due to altered hormone levels), compared with those using them exclusively for respiratory tract infections, adjusted for age and length of enrollment (odds ratio, 0.91; 95% confidence interval, 0.44-1.87).

Interestingly, women who used antibiotics to treat Acne or rosacca, which indicate risk factors for breast cancer because these conditions are related to hormone levels, were not found at elevated risk for breast cancer, compared with those using Antibiotic exclusively for respiratory tract infections.

The study concluded "Use of antibiotics is associated with increased risk of incident and fatal breast cancer."

The authors pointed out 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. Although further studies are needed, these findings reinforce the need for prudent long-term use of antibiotics."

It was several decades ago that the hypothesis that antibiotic use may boost the risk of breast cancer was first proposed.  One reason to support this hypothesis is that antibiotics disrupt the normal functions of intestinal micro flora to metabolize phytochemicals into compounds that can protect against cancer.
 
One early epidemiologic study conducted in Finland associated use of antibiotics with breast cancer risk.  The study found women used antibiotics to treat urinary tract infection were at 74% elevated risk for developing breast cancer, compared with those who did not use antibiotics for such a purpose.

The study further found no association between baseline bacteriuria and incidence of breast cancer during a follow-up suggesting that it is not the infection, but use of antibiotics may be responsible for the increase in the risk of breast cancer.

Breast cancer is expected to be diagnosed in 230,000 women each year in the United States and the disease and its complications kill about 37,000 annually in the country.  One in eight women are expected to develop the disease in their lifetime.

The current stud was based on data from Group Health Cooperative, a large health plan in Western Washington State.

The authors suggest that even though it is not 100% certain that use of antibiotics is the cause for the increased risk of breast cancer observed in their study, caution should be exercised and frequent use of antibiotics should be avoided. (David Liu, PHD)
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