Patterns of lymph node metastasis and prognosis in locally-advanced gastric cancer after neoadjuvant immunotherapy combined with chemotherapy.

Objective: To explore the pattern of lymph node metastasis and prognosis in locally advanced gastric cancer after neoadjuvant immunotherapy combined with chemotherapy (NICT). Methods: This retrospective study included pathologically confirmed gastric adenocarcinoma (cT3-4aN+) patients who underwent radical resection after ≥2 cycles of PD-1 inhibitor-based chemotherapy with complete postoperative pathology. Exclusions: distant/other metastases, non-R0 resection, Her-2+ with targeted therapy, microsatellite instability, or esophagogastric junction cancer invading >1 cm into lower esophagus. From January 2020 to December 2024, a total of 343 consecutive gastric cancer patients who received NICT treatment were admitted to Tianjin Medical University Cancer Institute and Hospital. According to the above criteria, 324 cases were included in the lymph node metastasis analysis, and 302 cases were included in the survival analysis. The median age of all patients was 58 years, with 245 males (75.6%) and a median body mass index (BMI) of 22.9 kg/m². There were 170 cases (52.5%) at T3 stage and 154 cases (47.5%) at T4a stage; the median number of cycles of neoadjuvant immunotherapy combined with chemotherapy was 3 cycles. The primary outcome measure was the positive lymph node metastasis rate (number of metastatic cases in the group / total number of dissected cases in the group×100%). A positive lymph node metastasis rate >10% was defined as high metastasis, and <5% as low metastasis. The secondary outcome measures were high-risk factors for lymph node metastasis and influencing factors related to patient prognosis. Lymph node grouping was performed according to the 8th edition of the American Joint Committee on Cancer (AJCC) guidelines. The positive lymph node metastasis rate was statistically analyzed by stratification based on surgical methods (total gastrectomy, proximal gastrectomy, distal gastrectomy). Multivariate analysis of risk factors for lymph node metastasis were performed with logistic regression analysis, and survival analysis were performed with the Kaplan-Meier method and Cox regression model. Results: The postoperative pathological complete response rate (pCR) of all patients was 21.0% (68/324), and the overall positive lymph node metastasis rate was 48.8% (158/324). A total of 150 patients underwent total gastrectomy, 42 underwent proximal gastrectomy, and 132 underwent distal gastrectomy.In the total gastrectomy group: the high metastasis subgroups were No.1 (19.3%, 29 cases), No.2 (14.7%, 22 cases), No.3 (28.0%, 42 cases), No.7 (12.7%, 19 cases), No.8a (16.0%, 24 cases), and No.9 (17.3%, 26 cases); the low metastasis subgroups were No.5 (4.7%, 7 cases), No.10 (3.3%, 5 cases), No.11d (1.3%, 2 cases), and No.12a (4.0%, 6 cases).In the proximal gastrectomy group: the high metastasis subgroups were No.3 (14.3%, 6 cases), No.7 (23.8%, 10 cases), and No.11p (11.9%, 5 cases); the low metastasis subgroups were No.4d (2.4%, 1 case) and No.10 (2.4%, 1 case).In the distal gastrectomy group: the high metastasis subgroups were No.3 (25.8%, 34 cases), No.6 (26.5%, 35 cases), No.7 (11.4%, 15 cases), and No.11p (11.4%, 15 cases); the low metastasis subgroups were No.4sb (3.8%, 5 cases) and No.12a (4.5%, 6 cases).Results of multivariate analysis showed that TRG grade (HR: 5.938, 95%CI: 3.028-11.646, P<0.001) was an independent factor affecting lymph node metastasis in patients with locally advanced gastric cancer after neoadjuvant immunotherapy combined with chemotherapy. The median follow-up time was 26.0 (6.0-54.3) months, and the 3-year overall survival (OS) of all patients was 78.1%. Results of multivariate Cox analysis showed that ypT (HR=1.744, 95%CI: 1.300-2.338, P<0.001), ypN (HR=1.998, 95%CI: 1.503-2.655, P<0.001), and postoperative complications (HR=1.913, 95%CI: 1.111-3.294, P=0.019) were independent factors affecting the overall survival of patients with locally advanced gastric cancer after neoadjuvant immunotherapy combined with chemotherapy. Conclusion: NICT significantly changes the pattern of lymph node metastasis in LAGC. ypT and ypN stages are core indicators for survival prognosis. The necessity of dissection for lymph node groups with a metastasis rate <5% needs to be carefully evaluated.