ERBB2 and cancer: Despite the widespread overexpression of HER2, the US FDA has only approved anti-HER2 therapy with anti-HER2 antibodies (trastuzumab and pertuzumab) for treatment of HER2-positive (HER2+) breast and gastroesophageal carcinomas because the antibody (Ab) therapies have not been found to be effective in other cancers.