A new study has reported that using birth control pills increases the risk of breast cancer in African-American women, especially the risk of triple negative disease. Triple negative breast cancer is a subtype of breast cancer that is estrogen receptor negative (ER-), progesterone receptor negative (PR-), and human epidermal growth factor receptor 2 (HER2) negative. Birth control pills have changed over time (with lower doses in newer formulations), making it worthwhile to examine the effect of more recent formulations on the risk of breast cancer.
Some previous studies have reported stronger positive associations between oral contraceptive use and ER- breast cancer than ER+ breast cancer. The present study represents the first evaluation of the effect of oral contraceptive use on the breast cancer risk by hormone receptor status among African-American women, a group with a higher rate of ER- breast cancer than the overall U.S. population.
The study included 53,848 participants in the Black Women's Health Study who were followed from 1995 to 2007. During this 12-year period, 789 new breast cancer cases were diagnosed among these women. The incidence of estrogen receptor negative cancer was 65 percent greater among women who had ever used oral contraceptives than among nonusers. Also, the risk of ER-/PR- breast cancer increased with increasing length of oral contraceptive use. In particular, the increase in risk was highest for women who had used oral contraceptives within the previous five years and whose use had lasted 10 or more years. The authors conclude that the oral contraceptive formulations used in recent decades increase breast cancer risk in African-American women, with a greater effect for ER- than ER+ cancer.