- Histologically confirmed diagnosis of metastatic TNBC; i.e. breast cancer that is estrogen receptor (ER) negative (=< 10%), progesterone receptor (PR) negative (=< 10%), and human epidermal growth factor receptor 2 (HER2) negative (0 or 1+ by immunohistochemistry or negative for gene amplification by fluorescence in situ hybridization [FISH])