Approximately, 15%‐25% of breast cancers consist of human epidermal growth factor 2 (HER2)‐overexpressing or HER2 amplified types.2 HER2‐targeted therapy, especially the anti‐HER2 antibody trastuzumab, has become the standard treatment for HER2‐positive breast cancer.3 Furthermore, another anti‐HER2 antibody pertuzumab was shown to significantly improve survival in patients with metastatic HER2‐positive breast cancer when combined with trastuzumab and docetaxel.4, 5 Pertuzumab can interrupt heterodimerization between HER2 and HER3, thereby preventing downstream signaling. The gene discussed is ERBB3; the disease is breast cancer.