ERBB2 and esophageal squamous cell carcinoma: OE21 cells as a member of the ESCC cell lines show high expression of EGFR forming mainly EGFR homodimers and only some EGFR/HER2 heterodimers, whereas OE33 cells as representative of EACs exhibit strong HER2 expression with the formation of HER2 homodimers and a lower amount of EGFR/HER2 heterodimers27.