3. Histologically -confirmed metastatic or unresectable TNB C that has either progressed on or after anthracycline- based chemotherapy or subject has refused anthracycline- based chemotherapy, or other taxane- and platinum- based therapies. TNBC is defined as breast cancer that lacks estrogen receptor (ER) and progesterone receptor (PR) expression, and human epidermal growth factor receptor 2 (HER2) overexpression and/or amplification. 4.