The copy number assay showed that EGFR and HER2 were amplified in 7% (16/244, one not determined; range 0.6–52.8 copies) and 11% (27/245; range 0.4–185.0 copies) of the ESCC specimens, respectively (Fig. 1A). Here, ERBB2 is linked to esophageal squamous cell carcinoma.