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According to a recent article published in the Journal of the American Medical Association, long-term antibiotic use may be associated with an increased risk of developing breast cancer.

Breast cancer claims the lives of approximately 40,000 women and is diagnosed in over 200,000 women annually in the United States alone. Researchers continue to evaluate possible associations between the development of breast cancer and environmental factors, so women may either alter their lifestyle to reduce or minimize the risk of developing breast cancer, or may undergo optimal screening if they are considered to be at a high risk of developing breast cancer due to environmental exposure of these risks. At present, some data has implicated the following environmental factors to be associated with either an increased or decreased risk of developing breast cancer in women: obesity, use of oral contraceptives, use of hormone replacement therapy, late age at birth of first child, diet, exercise, and smoking. In addition, an early age of first menstrual cycle, a late age of menopause and a higher number of menstrual cycles has been implicated in increasing the risk of developing breast cancer.

Researchers from the Fred Hutchinson Cancer Research Center in Seattle, Washington recently compiled data from several thousand women to evaluate a possible association between the use of antibiotics and the development of breast cancer. This study included 2,266 women with breast cancer who were older than 19 years of age, and nearly 8,000 women who did not have breast cancer (control group). Researchers included variables in their evaluation such as age of first birth, age of first menstruation, age of menopause, use of hormone replacement therapy, use of contraceptives, age, education, type of antibiotics used, number of different prescriptions of antibiotics, etc. Data indicated that women with the highest overall antibiotic use (over 1000 days), had over double the risk of developing breast cancer, and even women with the lowest antibiotic use (1-50 days) had a 40% increased risk of developing breast cancer. Furthermore, death from breast cancer was increased with the use of antibiotics.

The researchers concluded that long-term use of antibiotics may increase the risk of developing breast cancer. However, researchers do not rule out that the underlying causes resulting in the need for antibiotic use may play a role in the development of breast cancer, versus the antibiotics themselves. Furthermore, the researchers caution that patients should follow the instructions of their physician, should antibiotics be prescribed to them, and physicians should remain prudent in their dispensing of antibiotics.

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Reference: Velicer C, Heckbert S, Lampe J, et al. Antibiotic Use in Relation to the Risk of Breast Cancer.

Journal of the American Medical Association. 2004;291:827-835.