African American women who use oral contraceptives have a greater risk of developing breast cancer, according to a study published in Cancer Epidemiology Biomarkers and Prevention (2010 Aug;19(8):2073-9).

The 12-year study, conducted by investigators from the Slone Epidemiology Center at Boston University School of Medicine (BUSM), involved following 53,848 participants in the Black Women’s Health Study (BWHS), a large follow-up study of African American women from across the United States. Over the course of the study, researchers reported that 789 cases of breast cancer developed on which information on receptor status was obtained.

The study’s findings revealed that the incidence of estrogen receptor-negative cancer was 65% greater among women who had ever used oral contraceptives compared with those who never used oral contraceptives. Specifically, the increase in risk was greatest for women who had used oral contraceptives within the previous 5 years and whose use had lasted for 10 or more years. In addition, the increase was greater for estrogen receptor-negative than for estrogen receptor-positive breast cancer.

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“Some past studies found a stronger association with estrogen receptor-negative breast cancer. This was the first assessment of the effect of oral contraceptive use on the incidence of breast cancer classified by receptor status among African American women,” concluded lead investigator Lynn Rosenberg, PhD, an associate director of the Slone Epidemiology Center and professor of epidemiology at BUSM. “A mechanism to explain an adverse influence of oral contraceptives on development of estrogen receptor-negative breast cancer is currently unknown.”