Neoadjuvant Cadonilimab Combined With Perioperative Oxaliplatin Plus S1 for Diffuse or Mixed Type of Locally Advanced Gastric/Gastroesophageal Junction Adenocarcinoma

Cadonilimab: 10 mg/kg, iv, day 1 of every 3 weeks Oxaliplatin: 130 mg/m², iv, day 1 of every 3 weeks S1: 40-60 mg/m², po, day 1-14 of every 3 weeks (BSA \< 1.25 m², 40 mg \* 2/day, 1.25 m² ≤ BSA \< 1.5 m², 50 mg \* 2/day, BSA ≥ 1.5 m², 60 mg \* 2/day)

Placebo: iv, day 1 of every 3 weeks Oxaliplatin: 130 mg/m², iv, day 1 of every 3 weeks S1: 40-60 mg/m², po, day 1-14 of every 3 weeks (BSA \< 1.25 m², 40 mg \* 2/day, 1.25 m² ≤ BSA \< 1.5 m², 50 mg \* 2/day, BSA ≥ 1.5 m², 60 mg \* 2/day)