Molecularly targeted therapies for metastatic triple-negative breast cancer

Triple-negative breast cancer (TNBC) refers to a heterogeneous group of tumors that do not express the estrogen/progesterone-receptor (ER/PR), and human epidermal growth factor receptor-2 (HER2). TNBC is an aggressive histological subtype with limited treatment options and very poor prognosis following progression after standard chemotherapy regimens. There have been significant improvements in the outcome of other subtypes of breast cancer, including ER-positive/HER2 overexpressed tumors, attributed to the addition of targeted therapy, including hormonal agents and trastuzumab. However, no specific targeted agents are currently available for the treatment of TNBC. This review aims to collate and describe the most recent data on targeted therapies that have demonstrated efficacy in the management of metastatic TNBC. Targeted agents that have been investigated in the treatment of metastatic TNBC include inhibitors of poly(ADP-ribose) polymerase, angiogenesis, mammalian target of rapamycin, epidermal growth factor receptor, HDAC, Jak2, and Src. Several of these agents have shown considerable promise.