Systemic treatments of metastatic cancer have evolved considerably in the last two decades due to the incorporation of molecularly targeted treatments into first-line therapy, such as epidermal growth factor receptor (EGFR), anaplastic lymphoma kinase (ALK), and mesenchymal-epithelial transition (MET) pathway inhibitors for non-small-cell lung cancer (NSCLC) and HER2-active treatments for breast cancer. The gene discussed is ERBB2; the disease is breast carcinoma.