Challenging Clinical Scenarios: Treatment of Patients With Triple-Negative or Basal-Like Metastatic Breast Cancer

There is now compelling evidence to suggest that the biologic features of breast tumors affect response to specific therapies. Triple-negative breast cancer (TNBC) refers to a heterogeneous group of tumors that do not express the estrogen, progesterone, or HER2/neu receptors. By gene expression analysis, most (but not all) TNBCs are categorized as basal-like. TNBCs are often associated with particularly poor outcomes, with early development of chemotherapy resistance. There have been significant improvements in the outcome of other subtypes of breast cancer, including hormone receptor–positive/HER2+ 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 both cytotoxic and targeted therapies that have demonstrated efficacy in the management of metastatic TNBC. Evidence of response to various agents in early-stage breast cancer will be included, where relevant. Targeted agents that have been investigated in the treatment of TNBC include inhibitors of poly(ADP-ribose) polymerase, angiogenesis, mammalian target of rapamycin, epidermal growth factor receptor, and Src. Several of these agents have shown considerable promise.