Triple-negative breast cancer: making the most of a misnomer.

Triple-negative breast cancer (TNBC) is defined by its lack of (or minimal) estrogen receptor and progesterone receptor expression, together with the absence of human epidermal growth factor receptor 2 overexpression or gene amplification. It can be a particularly aggressive form of breast cancer, often characterized by early systemic relapse. This subtype, absent from traditional pathology classifications, has quietly crept into the oncologist's lexicon over the last decade and aroused considerable research interest. Based on tumor pathology, immunohistochemistry and gene profiling studies, TNBC is likely to represent a heterogeneous mix of breast cancer subtypes. This observation will have important implications for the selection of optimal therapies, which are yet to be defined. This article reviews recent insights in the classification and ontogeny of TNBC, current approaches to its management and promising therapeutic targets that are forming the basis for innovative early and late phase clinical trials.