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Women who recently used oral contraceptives had a 50% greater chance of developing breast cancer than that of women who formerly used or never used oral contraceptives, according to a case-control study published Aug. 1 in Cancer Research.
For the nested case-control study, the researchers compared 1,102 women aged 20-49 years who had been diagnosed with invasive breast cancer from 1990 to 2009 with 21, 755 controls sampled from the same health care delivery system, matched for age, year, enrollment length, and medical chart availability.
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Birth control pills and other oral contraceptives may raise the risk of developing breast cancer.
Oral contraceptive use within the prior year was associated with an increased breast cancer risk (odds ratio, 1.5; 95% confidence interval, 1.3-1.9) relative to never or former use of oral contraceptives, reported Dr. Elisabeth Beaber at the University of Washington, Seattle, and her associates.
Their findings suggest that risk may vary by oral contraceptive formulation. The investigators found significant associations between breast cancer and recent use of oral contraceptives involving high-dose estrogen (OR, 2.7; 95% CI, 1.1-6.2), ethynodiol diacetate (OR, 2.6; 95% CI, 1.4-4.7), or triphasic dosing with an average of 0.75 mg of norethindrone (OR, 3.1; 95% CI, 1.9-5.1). But other types of oral birth control, including low-dose estrogen oral contraceptives, were not associated with breast cancer (OR, 1.0; 95% CI, 0.6-1.7), Dr. Beaber and her associates noted (Cancer Res. 2014;74:4078-89).
"If confirmed, consideration of the breast cancer risk associated with different oral contraceptive types could impact discussions weighing recognized health benefits and potential risks," they concluded.
The study was funded by the National Cancer Institute. The authors reported no financial conflicts of interest.
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