Epidemiology of Health Disparities in Relation to the Biology of Estrogen Receptor-Negative Breast Cancer

Breast cancer is the most common cancer in women worldwide, accounting for just over 1 million new cases annually. Population-based statistics show that globally, when compared to whites, women of African ancestry tend to have more aggressive breast cancers that present more frequently as estrogen receptor-negative (ER−) tumors. ER− tumors fail to respond to current established targeted therapies, whether for treatment or prevention. Subsets of the ER− phenotype include those that are also negative for the progesterone receptor (PR) and human epidermal growth factor receptor (HER2); these are called “triple-negative” (TN) breast cancers. The ER−, TN, and basal-like phenotypic categories are important because they carry worse prognoses than estrogen receptor-positive (ER+) tumors, in addition to lacking obvious molecular targets for known therapies. Furthermore, among premenopausal women, the three subsets occur more frequently in women of African descent compared to white women with breast cancer. The contribution of these three subtypes of poor-prognosis tumors to the higher breast cancer mortality in black women is the focus of this review. Epidemiologic and lifestyle risk factors such as diet and physical activity and ER− breast cancer risk are reviewed. We will attempt to clarify some of the issues, in terms of their contribution to that component of health disparities that involves biological differences in breast cancer between women of African ancestry and white women.