Advances in Therapeutic Approaches for Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC), defined as breast cancer lacking expression of estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2 (HER2), accounts for up to 20% of all breast cancer, and it occurs at a higher frequency in younger, African American, and Hispanic women. Compared to breast cancers that are hormone receptor and/or HER2 positive, TNBC has an aggressive clinical course and worse prognosis. Because TNBC is by definition unresponsive to endocrine therapy (eg, tamoxifen, aromatase inhibitors) and HER2-directed therapies (eg, trastuzumab), chemotherapy continues to play an important role. TNBC constitutes a molecularly heterogeneous group of tumors that can vary in response to treatment, and clinical management can be challenging, particularly for the practicing community oncologist, for whom breast cancer may be only one of many tumor types encountered. In January 2020, the Breast Cancer Therapy Expert Group (BCTEG) convened a roundtable discussion on the topic of advances in the treatment of TNBC. Topics discussed included histopathologic classification/definition of TNBC, neoadjuvant strategies, adjuvant chemotherapy (with special emphasis on management of patients who do not experience a pathologic complete response), and treatment of metastatic disease. Also reviewed was the wide range of emerging pathways and therapies currently under investigation to expand TNBC treatment options, including immunotherapies and poly(ADP-ribose) polymerase (PARP) inhibitors. This article summarizes the BCTEG discussion and highlights the key opinions relating to the treatment of patients with TNBC.