ERBB2 and gastroesophageal junction adenocarcinoma: HER2-targeting mAbs are also approved for various oncologic indications, though they target slightly different epitopes as follows: trastuzumab (humanized mAb approved for BC, GC, and gastroesophageal junction adenocarcinoma; binds HER2 ECDII), pertuzumab (humanized mAb approved for BC; binds HER2 ECDII separate from trastuzumab), and margetuximab (mouse/human chimeric Fc-modified mAb approved for BC; binds same HER2 ECDII as trastuzumab) [57,58].