(CNN) A new study may better explain why African American women have greater risk for developing more aggressive and difficult-to-treat forms of breast cancer, called estrogen and progesterone receptor negative cancers (ER-/PR-). The findings appear in the journal Cancer Epidemiology, Biomarkers and Prevention.
Breast cancer is the second-most common type of cancer among women, after skin cancer. While white women are slightly more likely to get breast cancer than African American women, African American women are more likely to die from breast cancer, according to the American Cancer Society, because they are more likely to develop more aggressive breast cancers. But why this happens has been less clear.
Researchers at Boston University's Slone Epidemiology Center analyzed data from the Black Women's Health Study, which began in 1995 and follows 59,000 African American women who complete health questionnaires every two years.
From 1995 to 2009, 457 women developed estrogen and progesterone receptor positive cancers, ER+/PR+.