ERBB2 and esophageal squamous cell carcinoma: Using two well characterized esophageal cancer cell lines, OE21 as a typical esophageal squamous cell carcinoma (ESCC) showing high expression of EGFR and OE33 esophageal adenocarcinoma (EAC), characterized by high expression of HER2, we established a model system to study the specificity of engineered toxins directed to surface molecules, which are highly expressed on several tumor cells.