ERBB2 and breast cancer: Breast cancer patients who are both hormone receptor (HR)‐negative and HER2‐negative account for 15%‐20% of all breast cancers diagnosed in the United States (US).1, 2 Compared to patients with HR‐positive or HER2‐positive tumors where average survival exceeds 50 months survival for women with metastatic triple‐negative breast cancer (mTNBC) is considerably shorter ranging from 11 to 17.8 months.3, 4, 5, 6 The lower survival for mTNBC patients reflects the limited treatment options available when endocrine or HER‐2 targeting therapy is not an option.