Health disparities in breast cancer: biology meets socioeconomic status

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 (AA) tend to have more aggressive breast cancers that present more frequently as estrogen receptor negative (ERneg) tumors. ERneg tumors fail to respond to current established targeted therapies, whether for treatment or prevention. Subsets of the ERneg phenotype include those that are also negative for the progesterone receptor (PR) and HER2; these are called triple negative'' (TN) breast cancers. TN tumors frequently have pathological characteristics resembling basal-like'' breast cancers. Hence, the latter two terms are often used interchangeably; yet, despite extensive overlap, they are not synonymous. The ERneg, TN, and basal-like phenotypic categories are important because they carry worse prognoses than ER-positive (ERpos) tumors, in addition to lacking obvious molecular targets, such as HER2 and the ER, 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. We will attempt to clarify some of the issues, including risk factors, in terms of their contribution to that component of health disparities that involves biological differences in breast cancer between women of AA and white women.