In particular, while gefitinib, a first-generation TKI, was effective only on esophageal cancer patients with EGFR copy number gain (39), EGFRe1 silencing is effective in both KYSE-30 and -150 cells, which suggests that inhibiting EGFRe1 can be considered to treat a wider spectrum of ESCC types with high EGFR levels obtained not only by gene copy number gain but also by protein overexpression. Here, EGFR is linked to esophageal squamous cell carcinoma.