Targeting triple-negative breast cancer: optimising therapeutic outcomes

Triple-negative breast cancer (TNBC) is a distinct subset of breast cancer (BC) defined by the lack of immunohistochemical expression of the estrogen and progesterone receptors and human epidermal growth factor receptor 2. It is highly heterogeneous and displays overlapping characteristics with both basal-like and BC susceptibility gene 1 and 2 mutant BCs. This review evaluates the activity of emerging targeted agents in TNBC. A systematic review of PubMed and conference databases was carried out to identify randomised clinical trials reporting outcomes in women with TNBC treated with targeted and platinum-based therapies. Our review identified TNBC studies of agents with different mechanisms of action, including induction of synthetic lethality and inhibition of angiogenesis, growth, and survival pathways. Combining targeted agents with chemotherapy in TNBC produced only modest gains in progression-free survival, and had little impact on survival. Six TNBC subgroups have been identified and found to differentially respond to specific targeted agents. The use of biological preselection to guide therapy will improve therapeutic indices in target-bearing populations. Ongoing clinical trials of targeted agents in unselected TNBC populations have yet to produce substantial improvements in outcomes, and advancements will depend on their development in target-selected populations.