Study finds oral contraceptives dont increase risk of breast cancer

About the study

Researchers from several U.S. institutions collaborated on this case-control study, called the Women’s Contraceptive and Reproductive Experiences (Women’s CARE) Study. They enrolled 9257 women between the ages of 35 and 64 from the following U.S. regions: Atlanta, Detroit, Philadelphia, Los Angeles, and Seattle. Cases were 4575 women with breast cancer diagnosed between 1994 and 1998. Controls were 4682 women living in the same geographic area who did not have breast cancer. Controls were also matched to cases on the basis of age and race.

Participants were interviewed in person using a standardized questionnaire about oral contraceptive use, other hormone therapies, reproductive history, medical history, and family medical history.

Researchers compared the number of breast cancer cases among women who took oral contraceptives with the number of cases among nonusers.

The findings

Women who had taken oral contraceptives at any time in their lives were no more likely to develop breast cancer than women who never took oral contraceptives. Even among women with a family history of breast cancer, the risk did not differ among users and nonusers.

In calculating these statistics, the researchers accounted for other risk factors for breast cancer, such as age, family history of breast cancer, age at first menstruation, age at menopause, age at first pregnancy, number of pregnancies, race, menopausal status, and use of hormone replacement therapy.

Although these results are interesting, there are limitations to this study.

First, participants had to recall details of their oral contraceptive use and reproductive history that may have occurred years in the past. Therefore, the accuracy of the information may have been compromised. Second, researchers did not collect any information about dietary habits or exposure to radiation and toxic chemicals—two factors that may affect the risk of breast cancer. Third, this study included only white women and black women so more research is needed in women of other ethnic groups. Fourth, we don’t know if any of the participants had a BRCA gene mutation (which increases breast cancer risk), so we cannot draw any conclusions about the risk of breast cancer among women with a BRCA gene who take oral contraceptives. Finally, the number of women over age 40 taking oral contraceptives (as a form of hormone replacement therapy) was small. More research is needed to determine the risks and benefits associated with this particular use of oral contraceptives.

How does this affect you?

Does this mean you will not develop breast cancer if you take oral contraceptives? Not necessarily. Aside from genetic testing, there is no way to predict whether or not a woman might develop breast cancer. However, these findings support the findings of other studies that oral contraceptives do not increase your risk of developing breast cancer later in life.

On the other hand, these findings contradict the findings of a pooled analysis of many studies on oral contraceptive use and breast cancer, which suggested that women who had taken oral contraceptives were at slightly higher risk than nonusers within the first 10 years after taking the pills. In this analysis (called a meta-analysis), the researchers collected data from numerous studies and analyzed it together in an attempt to derive an overall estimate of risk. Because studies are designed differently, meta-analyses lack a certain degree of precision, though they do help to synthesize data from many similar studies.

If you are at increased risk for breast cancer, talk with your health care provider about your risk for breast cancer and whether or not oral contraceptives are a suitable form of contraception for you.