Different Cycles of Neoadjuvant PD-1 Blockades + Chemotherapy for Advanced Gastric Cancer

The goal of this observational study is to analyze the impact of different durations of neoadjuvant PD-1 inhibitor combined with chemotherapy on tumor regression and safety in patients with advanced gastric cancer. The main questions it aims to answer are: * Does the duration of neoadjuvant treatment influence tumor regression grading (TRG)? * How does treatment duration affect perioperative safety and clinical outcomes? Participants who have previously undergone neoadjuvant PD-1 inhibitor combined with chemotherapy followed by surgery as part of their routine medical care will have their clinical data retrospectively reviewed and analyzed.