Trastuzumab Deruxtecan for Subjects With HER2-Positive Gastric Cancer or Gastro-Esophageal Junction Adenocarcinoma After Progression on or After a Trastuzumab-Containing Regimen (DESTINY-Gastric04)

Adults (according to local regulation) and able to provide informed consent for study participation.Pathologically documented gastric and GEJ adenocarcinoma that has been previously treated in the metastatic setting (unresectable, locally advanced, or metastatic disease). Progression on or after first-line therapy with a trastuzumab or approved trastuzumab biosimilar-containing regimen. Note: Prior neoadjuvant or adjuvant therapy with a trastuzumab-containing regimen can be counted as a line of therapy if the subject progressed on or within 6 months of completing neoadjuvant or adjuvant therapy. Prior neoadjuvant or adjuvant therapy that does not include trastuzumab will not be counted as a line of therapy regardless of the progression status of the subject. Locally or centrally confirmed HER2-positive (IHC 3+ or IHC 2+ and evidence of HER2 amplification by ISH) as classified by ASCO-CAP on a tumor biopsy obtained after progression on or after a first-line trastuzumab or approved trastuzumab biosimilar-containing regimen. Eastern Cooperative Oncology Group performance status of 0 or 1 at Screening. Adequate bone marrow, renal, hepatic function, and blood clotting function within 14 days of randomization.