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Certain birth control pills increase breast cancer risk

The study group comprised 1,102 women aged 20 through 49 years who were diagnosed with invasive breast cancer from 1990 through 2009
The study group comprised 1,102 women aged 20 through 49 years who were diagnosed with invasive breast cancer from 1990 through 2009Robin Wulffson, MD

According to a new study, certain birth control pills are associated with an increased risk of breast cancer. The findings were published on August 1 in the journal Cancer Research by investigators at: the Group Health Research Institute, Group Health Cooperative; the Fred Hutchinson Cancer Research Center; and the University of Washington, all in Seattle, Washington.

The study authors note that previous studies of oral contraceptives and breast cancer have reported that their use slightly increases risk; however, most studies relied on self-reported use and did not examine current birth control pill formulations. Therefore, they conducted a study of female enrollees in a large United States integrated healthcare delivery system. The study group comprised 1,102 women aged 20 through 49 years who were diagnosed with invasive breast cancer from 1990 through 2009. Control patients 921,952 women) were randomly selected from enrollment records and matched to the breast cancer cases for age, year, enrollment length, and medical chart availability. Detailed oral contraceptive use information was obtained from electronic pharmacy records and subjected to statistical analysis..

The researchers found that recent oral contraceptive use (within the prior year) was associated with an increased breast cancer risk (1.5-fold increased risk compared to never or former oral contraceptive use. The association was stronger for estrogen receptor–positive (1.7-fold increased risk) than estrogen receptor–negative (1.2-fold increased risk); however, the difference was not statistically significant. Recent use of birth control pills containing high-dose estrogen (2.7-fold increased risk), ethynodiol diacetate (2.6-fold increased risk), or triphasic dosing with an average of 0.75 mg of norethindrone (3.1-fold increased risk) was associated with particularly elevated risks. However, other types, including low-dose estrogen oral contraceptives, were not (risk: 1.0)).

The investigators concluded that their study suggests that recent use of contemporary oral contraceptives is associated with an increased breast cancer risk, which may vary by formulation. They note that if their findings are confirmed by future studies, evaluation of the breast cancer risk associated with different oral contraceptive types should be made that weighed the health benefits against the potential risks.

Take home message:

Currently available oral contraceptives are significantly safer than older versions because their hormonal content is significantly less. It would be prudent to check the label on your current oral contraceptive packet to determine whether it is among the high-risk types. If so, discuss, changing to a different pill with your gynecologist or family physician. Women with a family history of breast cancer and/or carry the BRCA1 or BRCA2 gene are at increased risk for breast cancer regardless of whether they take oral contraceptives. However, taking an oral contraceptive might increase that risk.

The authors determined that taking oral contraceptives was associated with a 50% increase in risk of breast cancer for women similar to those in the study, who were between ages 20 and 49. According to the American Cancer Society, less than 1% of women will get breast cancer before age 40; thus, even with a 50% that number would still be less than 1%.