Trastuzumab deruxtecan (T-DXd) 6·4 mg/kg is approved in several countries worldwide for the treatment of advanced HER2+ gastric or GEJ adenocarcinoma in patients who have received a prior trastuzumab-based regimen, and in Japan for patients with HER2+ advanced gastric cancer that has progressed after chemotherapy. This evidence concerns the gene ERBB2 and gastric cancer.