Lymph Node Metastasis Pattern After Neoadjuvant Chemoimmunotherapy in LAGC

The purpose of this observational study is to learn how stomach cancer that has spread to nearby lymph nodes responds to standard chemotherapy combined with immunotherapy given before surgery. In people with locally advanced gastric cancer, this pre-surgery treatment can shrink the tumor and clear cancer cells from some lymph nodes. However, it is not clear which groups of lymph nodes around the stomach still contain cancer cells after treatment. The study will also examine whether dense scarring (fibrosis) around the tumor is linked to a lower chance of cancer remaining in the lymph nodes. This information may help doctors in the future decide whether some lymph node groups can be safely left in place during surgery for people with severe scarring. Participants in this study will receive standard pre-surgery treatment with SOX chemotherapy (S-1 plus oxaliplatin) and a PD-1 inhibitor for at least 2 cycles. After treatment, they will undergo standard gastrectomy with D2 lymph node dissection, which is the routine surgical removal of the main lymph node groups around the stomach. During surgery, the surgeon will record the degree of scarring and difficulty in separating the tissues. Lymph nodes will be collected and labeled by station so that each group can be examined separately. The study will then describe how often cancer is found in each lymph node station after treatment and explore whether scarring is related to cancer remaining in the nodes. The study will also track surgical outcomes and follow participants for up to 3 years to assess cancer recurrence and survival. Approximately 103 participants will be enrolled. The study is expected to run from January 2027 through December 2029. Each participant will be followed for about 3 years after surgery, with clinic visits every 3 months for the first 2 years and every 6 months in the third year. This study does not assign participants to different treatments; all participants receive standard care, and the study only observes and records the results.

Inclusion Criteria: * Age ≥ 18 years, regardless of gender * Gastric adenocarcinoma pathologically confirmed by gastroscopic biopsy, with a clinical stage of cT3-4aN+M0 * Standardized completion of neoadjuvant chemotherapy combined with immunotherapy for the scheduled cycles (≥ 2 cycles) * Planned for or have undergone standard D2 radical gastrectomy following the completion of neoadjuvant therapy * The number of harvested lymph nodes in the postoperative specimen is ≥ 16, and the pathology report can clearly distinguish the metastasis status of lymph nodes in each anatomical station, providing complete station-specific pathological data * Patients volunteer to participate in this study and have signed a written informed consent form Exclusion Criteria: * Pathologically confirmed non-gastric adenocarcinoma, such as gastric squamous cell carcinoma, neuroendocrine tumors, or metastatic gastric tumors * Advanced patients with distant metastasis that precludes radical gastrectomy * Patients who have received prior preoperative anti-tumor treatments other than the study protocol, such as radiotherapy, targeted therapy, chemotherapy alone, or monotherapy immunotherapy; or patients with a previous history of gastric surgery or other malignancies * Patients who experience disease progression, severe immune-related adverse events, or chemotherapy intolerance leading to treatment termination during neoadjuvant therapy, or those complicated with severe organ failure (e.g., heart, liver, kidney, lung) rendering them unable to undergo radical surgery * Cases where a standard D2 radical gastrectomy was not performed, the extent of lymph node dissection was insufficient, the number of dissected lymph nodes was \< 16, or the pathology report lacks data on station-specific lymph node metastasis, precluding statistical analysis * Missing clinical data or poor compliance with follow-up, posing a high risk of loss to follow-up