Oral contraceptive use associated with increased risk of breast cancer

Investigators from the Slone Epidemiology Center at Boston University School of Medicine (BUSM) have reported that African American women who use oral contraceptives have a greater likelihood of developing breast cancer than nonusers. The study results, recently published on-line in Cancer Epidemiology Biomarkers and Prevention, were based on data from the Black Women's Health Study (BWHS), a large follow-up study of 59,000 African American women from across the U.S. conducted by investigators at the Slone Epidemiology Center since 1995.

The investigators followed 53,848 participants in the BWHS for 12 years, during which time 789 cases of breast cancer developed on which information on receptor status was obtained. The incidence of estrogen receptor negative cancer was 65 percent greater among women who had ever used oral contraceptives than among nonusers.

According to the BUSM researchers, the increase in risk was greatest for women who had used oral contraceptives within the previous five years and whose use had lasted 10 or more years, and the increase was greater for estrogen receptor negative than for estrogen receptor positive breast cancer. Estrogen receptor positive tumors have a better prognosis than estrogen receptor negative breast cancers.

Lead investigator Lynn Rosenberg, PhD, an associate director of the Slone Epidemiology Center and professor of epidemiology at BUSM, points out- that oral contraceptive formulations have changed over time, making it relevant to assess the effects of more recent formulations on breast cancer risk. "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," said Rosenberg who is also the principal investigator of the BWHS. "A mechanism to explain an adverse influence of oral contraceptives on development of estrogen receptor negative breast cancer is currently unknown," she added.