ERBB2 and gastroesophageal junction adenocarcinoma: Most of the tumors were serous (65.9%); only seven cases were clear cell.5 Although trastuzumab alone may not be effective, there is interest in fam-trastuzumab deruxtecan-nxki (Enhertu, T-DXd, DS-8201a), which is US Food and Drug Administration–approved for metastatic breast cancer, non–small cell lung cancer, and gastric or gastroesophageal junction adenocarcinoma.6 This compound is an antibody-drug conjugate (ADC) consisting of an anti-HER2 antibody linked to a topoisomerase I inhibitor, and designed to deliver a potent cytotoxic payload to HER2-expressing tumor cells.