Risk of Triple-Negative Breast Cancer

Breast cancer is a heterogeneous disease that can be divided into distinct subtypes based on patterns of gene expression (1–3) or tumor marker staining (3–5). This biological heterogeneity trans-lates to important clinical differences (2,4–9) and likely reflects etiologic differences (10,11). One tumor subtype that has emerged as being of particular clinical and public health significance is triple-negative breast cancer. Triple-negative breast cancers, which account for 10%–25 % of invasive breast cancers (8,9,12–16), are characterized by a lack of estrogen receptor (ER), progesterone receptor (PR), and HER2 expression and typically exhibit a basal-like pattern of gene expression (1,17,18). The triple-negative phe-notype is associated with an aggressive pathology and poorer prognosis than the predominant ER-positive (ER+) phenotype (4,5,7–9), and there are currently no targeted therapies for the treatment of triple-negative breast cancer. If the molecular profile