ESCAT Tier I is the highest level of evidence indicating a list of ready-for-routine-use biomarkers that includes EGFR, BRAF V600E, and MET exon 14-skipping mutations and ALK, ROS1, RET, and NTRK fusions for non-small cell lung cancer (NSCLC); examples of other Tier I biomarkers are ERBB2 amplifications, PIK3CA and BRCA1/2 germline mutations, and microsatellite instability (MSI)-high for breast cancer and IDH1 and BRAF mutations, MSI-high, human epidermal growth factor receptor 2 (HER2) overexpression, and FGFR2 and NTRK fusions for cholangiocarcinoma [2,8]. The gene discussed is ERBB2; the disease is breast cancer.