Phase 2 Study of Trastuzumab Deruxtecan in the Neoadjuvant Treatment, or Trastuzumab Deruxtecan Plus Capecitabine Plus Durvalumab(MEDI4736) in the Preoperative and Postoperative Adjuvant Treatment for Patients with HER2 Positive Gastric and Gastroesophageal Junction Adenocarcinoma

T-DXd will be administered at a dose of 6.4 mg/kg (decimal) by intravenous infusion every 21 days (3 weeks) for subsequent three cycles.

Administer each cycle over 21 days. T-DXd is administered by intravenous infusion at 5.4 mg/kg every 21 days (every 3 weeks). Capecitabine is given at 750 mg/m2 BID, taken orally for 14 days, followed by a drug holiday from the evening of Day 15 to the morning of Day 22 (Day 1 of the next cycle). Durvalumab is administered at 1500 mg by intravenous infusion over 60 minutes every 21 days (every 3 weeks). As neoadjuvant chemotherapy, administer T-DXd, Capecitabine, and Durvalumab in combination on a q3w schedule for 3 cycles. As adjuvant chemotherapy consists of T-DXd, Capecitabine, and Durvalumab in combination on a q3w schedule for 3 cycles, followed by Durvalumab monotherapy on a q4w schedule until 10 cycles are completed.