Triple Negative Breast Cancer—Review of Current and Emerging Therapeutic Strategies

T riple negative breast cancer (TNBC) is associated with a poor prognosis compared to other types of breast cancer. The classification of 'triple negative' is not one homogenous tumor type, but rather is made up of multiple molecularly and biologically diverse tumor subtypes. At present, no approved targeted therapy exists and the standard remains cytotoxic chemotherapy. The identification of TNBC subtypes has provided a basis for identifying possible targeted therapeutic options. In addition, the recognition that some TNBCs share characteristics similar to tumors arising in patients with germline BRCA mutations has led to consideration of DNA damaging agents as a potential treatment option. Multiple investigational approaches are also underway, including immune checkpoint inhibition, poly (ADP-ribose) polymerase inhibition, and androgen receptor blockage. The limited options available for systemic treatment of TNBC will hopefully expand as more is learned about the complex biology and molecular targets of this group of breast cancers. This review will discuss the biology of TNBC, current treatment options, and promising experimental strategies.