Triple-negative breast cancer: molecular features, pathogenesis, treatment and current lines of research

Breast cancer is a heterogeneous disease with different morphologies, molecular profiles, clinical behaviour and response to therapy. The triple negative is a particular type of breast cancer defined by absence of oestrogen and progesterone receptor expression as well as absence of ERBB2 amplification. It is characterized by its biological aggressiveness, worse prognosis and lack of a therapeutic target in contrast with hormonal receptor positive and ERBB2+ breast cancers. Given these characteristics, triple-negative breast cancer is a challenge in today's clinical practice. A new breast cancer classification emerged recently in the scientific scene based in gene expression profiles. The new subgroups (luminal, ERBB2, normal breast and basal-like) have distinct gene expression patterns and phenotypical characteristics. Triple-negative breast cancer shares phenotypical features with basal-like breast cancer, which is in turn the most aggressive and with worse outcome. Since microarray gene-expression assays are only used in the research setting, clinicians use the triple-negative definition as a surrogate of basal-like breast cancer. The aim of this review, that focuses on triple-negative breast cancer, is to summarize the most relevant knowledge on this particular type of cancer in terms of molecular features, pathogenesis, clinical characteristics, current treatments and the new therapeutic options that include the use of platinum compounds, EGFR antagonists, antiangiogenics and PARP inhibitors. Advances in research are promising and new types of active drugs will become a reality in the near future, making possible a better outcome for this subgroup of breast cancer patients.