What is the difference between triple-negative and basal breast cancers?

Triple-negative breast cancer (TNBC) represents a phenotype defined by the lack of estrogen receptor, progesterone receptor, and human epidermal growth factor receptor-2 expression. Because TNBCs have more aggressive features and lack a therapeutic target, they have become a key topic of clinical and research interest within the oncology community. With advancements in the field of molecular biology, gene expression profiling has resulted in the identification of intrinsic subtypes including basal-like breast cancers (BLBCs). Although often thought to be synonymous, TNBC and BLBC represent different biologic phenomena. Furthermore, even within the basal-like subtype, diversity exists. The purpose of this review is to outline the most current evidence in an attempt to answer the question: what is BLBC?