Perioperative Therapies in Locally Advanced Unresectable Gastric Cancer

Gastric cancer (GC) is the fifth most commonly diagnosed cancer, with over one million cases diagnosed annually worldwide. Human epidermal growth factor receptor 2 (HER2) overexpression in GC (seen in 4.4% to 53.4% of patients in different reports) is predictive biomarker of response to HER2-targeting therapies. Trastuzumab in combination with cisplatin or oxaliplatin, and a fluoropyrimidine (capecitabine or 5-fluorouracil \[5-FU\]), is approved anti-HER2 therapy for first-line treatment of HER2-positive gastric or gastroesophageal junction (GEJ) cancer. Rilvegostomig 750 mg Q3W was selected as recommended Phase 2 dose based on all available ARTEMIDE-01 clinical safety, efficacy, PK, RO data as well as modeling analysis. The dose of 750 mg Q3W is predicted to achieve intra-tumoral RO of ≥ 90% in the majority of participants across a broad spectrum of conditions. This is a phase II study to initially assess the efficacy of perioperative Trastuzumab Deruxtecan (T-DXd) and Capecitabine combination with or without Rilvegostomig in patients with HER2 positive locally advanced unresectable GC and potentially by subsequent protocol amendment in HER2 low locally advanced GC. Other agents may also subsequently be assessed in this protocol, by protocol amendments

Neoadjuvant therapy will begin following completion of the screening period, and patients will undergo resection surgery 4 to 8 weeks after the last dose of neoadjuvant therapy. Surgery \>8 weeks after the last dose of neoadjuvant therapy may be permitted in consultation with the Sponsor. Adjuvant therapy will begin 4 to 12weeks post-surgery (based on the patient's recovery period). Tumor evaluation using modified RECIST 1.1 will be conducted at screening (within 28 days prior to first dose) and ≤28 days after last dose of neoadjuvant therapy and after surgery. Every 12 weeks (±1 week) relative to the Adjuvant Baseline scan for first years and then every 24 weeks (±2 week) until progression/recurrence The imaging modalities used for modified RECIST 1.1 assessment will be CT or MRI scans of chest, abdomen and pelvis. Modified RECIST 1.1 scans will be analyzed by the investigator on site.