For example, EGFR activating mutation for EGFR-TKIs in lung cancer [12–14], c-met amplification in lung cancer for MET-TKI [13], ALK fusion for ALK-TKI in lung cancer [15], HER2 amplification in gastric and breast cancers for Herceptin®, etc. In contrast, there are few epigenetic predictive biomarkers, e.g. gene expression in mRNA, that were validated for reasons to be elucidated. The gene discussed is ERBB2; the disease is lung cancer.