Long-term use of antibiotics possibly linked with increased risk of breast cancer

02/12/04

JAMA Embargo Lifted Immediately for study on "Antibiotic Use in Relation to the Risk of Breast Cancer" by Dr. Velicer et al and the accompanying editorial, "Antibiotics and Breast Cancer - What is the Meaning of This?" by Drs. Ness and Cauley in this week's issue of JAMA.

It has come to our attention that the embargo for these two JAMA articles (which was set for tomorrow, February 17 at 3 p.m. central time) was broken with a story published yesterday. Because this information has now been made public, we are immediately lifting the embargo on these two reports, so that other media outlets also can release the story now (and do not have to wait until the scheduled time of lifting the embargo). The rest of the February 18 issue remains embargoed until 3 p.m. central time, Tuesday, February 17.

The JAMA editors thank all of the journalists who abide by the JAMA/Archives embargoes each week. Please call or email the JAMA/Archives media relations department at 312-464-JAMA or mediarelations@jama-archives.org, if you have questions.

CHICAGO – Women who used increased amounts of antibiotics appear to have a greater risk of breast cancer, according to a new study in the February 18 issue of The Journal of the American Medical Association (JAMA). However, the researchers point out that more studies are needed to determine if the association between breast cancer and antibiotics is causal or if there are other underlying factors to be considered.

"Breast cancer is the most frequently diagnosed nonskin malignancy and the second leading cause of cancer mortality in U.S. women," according to background information from the authors. "It is also the most common cancer in women worldwide, with more than 1 million cases diagnosed each year. Antibiotics are used extensively and overused in many countries, though efforts are underway to curb overuse."

Christine M. Velicer, Ph.D., from the University of Washington, Seattle, and colleagues, examined the association between use of antibiotics and the risk of breast cancer by reviewing medical data from 10,219 women enrolled at Group Health Cooperative (GHC), a large nonprofit health plan in western Washington State. (Dr. Velicer is now on staff at the GHC Center for Health Studies, Seattle.) The study cases included 2,266 women older than 19 years with primary, invasive breast cancer enrolled in the health plan, and 7,953 randomly selected female health plan members who did not have breast cancer in the control group. Data on antibiotic use were obtained from the GHC pharmacy database. The researchers looked at the cumulative number of days of antibiotic use and the total number of antibiotic prescriptions for each study participant.

"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," the researchers state. For example, compared to women who had used no antibiotics, the researchers found that women who had cumulatively used antibiotics for 1 – 500 days had an associated increased risk of about one-and-a-half times of incident 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. All classes of antibiotics were associated with increased risk." The researchers also looked at a subset of study participants with heavy use of macrolide and tetracycline antibiotics and found no difference in risk of incident breast cancer among women using these antibiotics for acne and/or rosacea compared with women using these drugs for respiratory tract infections.

In conclusion, the authors write: "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 and the need for further studies of the association between antibiotic use and cancer risk."

(JAMA. 2004;291:827-835. Available post-embargo at JAMA.com)

Source: Eurekalert & others

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