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.

Inclusion Criteria: * Non-bedridden patients aged 18-90 years; * Histologically confirmed gastric or gastroesophageal junction adenocarcinoma by biopsy; * Evaluated as resectable advanced gastric cancer via CT, MRI, or laparoscopic exploration; * No prior anti-tumor treatments such as chemotherapy, radiotherapy, or immunotherapy; * No history of other malignancies within the past 5 years; * Received at least one cycle of PD-1 inhibitor combined with chemotherapy preoperatively, with no restrictions on the specific PD-1 inhibitor or chemotherapeutic agents; * Underwent radical gastrectomy after neoadjuvant therapy; * No severe underlying diseases. Exclusion Criteria: * Incomplete or inaccessible clinical and pathological data; * Postoperative pathology confirming non-gastric or non-gastroesophageal junction adenocarcinoma; * Distant metastases present prior to treatment; * Concurrent diagnosis of other malignancies.