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.

CHICAGO—The effectiveness of the chickenpox vaccine decreases significantly in the first year after vaccination, and also appears lower if the vaccine is administered to children younger than 15 months of age, according to a study in the February 18 issue of the Journal of the American Medical Association (JAMA).

According to background information in the article, chickenpox (varicella) vaccine is recommended for routine administration to healthy children at 12 to 18 months of age and to older children who have not yet had chickenpox. Recent reports of outbreaks of chickenpox in groups with substantial rates of immunization have increased concern about the effectiveness of the current recommendations for administration of the vaccine.

Marietta Vazquez, M.D., of the Yale University School of Medicine, New Haven, Conn., and colleagues examined the influence of age at the time of chickenpox vaccination and the time since vaccination on the vaccine's effectiveness. The study, conducted from March 1997 through June 2003, included 339 children 13 months or older who were clinically diagnosed as having chickenpox. For each case subject, two controls were selected, matched by both age and pediatric practice.

The researchers found that although the overall effectiveness of the vaccine was 87 percent, there was a substantial difference in the vaccine's effectiveness in the first year after vaccination (97 percent) and in years 2 to 8 after vaccination (84 percent). "The vaccine's effectiveness in year 1 was substantially lower if the vaccine was administered at younger than 15 months (73 percent) than if it was administered at 15 months or older (99 percent), although the difference in effectiveness overall for children immunized at younger than 15 months was not statistically significantly different than for those immunized at 15 months or older (81 percent vs. 88 percent). Most cases of chickenpox in vaccinees were mild," the authors write.

CHICAGO—Established cardiovascular disease risk factors, including high blood pressure, smoking, diabetes, and obesity are associated with the development of kidney disease, according to a study in the February 18 issue of the Journal of the American Medical Association (JAMA).

According to background information provided by the authors, "hypertension and diabetes are the leading causes of end-stage renal disease (ESRD). Among individuals who develop ESRD, the risk of cardiovascular disease is 10 to 20 times higher than the general population, and increased risks are evident even in mild kidney disease." The authors state there are approximately 275,000 patients with ESRD in the U.S. and an estimated 8 million additional U.S. adults have kidney disease.

Caroline S. Fox, M.D., M.P.H., from the National Heart, Lung, and Blood Institute's Framingham Heart Study, Framingham, Mass., and colleagues identified predictors of the development of new-onset kidney disease. The researchers analyzed data from 1,223 men and 1,362 women in the Framingham Offspring Study who had a baseline (initial) examination in 1978 - 1982 and returned for a follow-up examination in 1998 - 2001. None of the participants had kidney disease in the initial examinations. After an average follow-up of 18.5 years, 244 participants (9.4 percent) had developed kidney disease. The researchers defined kidney disease as a decrease in glomerular filtration rate (GFR) [the rate at which the kidneys filter waste] to the fifth percentile or lower, based on national definitions.

ANTIBIOTICS & BREAST CANCER