ERBB2 and cancer: With no known ligand to date, HER2 can be activated by heterodimerization with other members of the EGFR family or by homodimerization when overexpressed on the cell surface.24,25 HER2 overexpression has been described in a wide variety of cancers, including breast, ovarian, colon, bladder, gastric, uterine cervix, head and neck, esophageal cancer, melanoma, and non-small cell lung cancer,24,26,27,28 making HER2 a well-established therapeutic tumor target.