Background: Peritoneal metastasis is the most common metastasis pattern of gastric cancer. Patients with gastric cancer peritoneal metastasis (GCPM) have a poor prognosis and respond poorly to conventional treatments. Recently, immune checkpoint blockade (ICB) has demonstrated favourable efficacy in the treatment of GCPM. Stratification of best responders and elucidation of resistance mechanisms of ICB therapies are highly important and remain major clinical challenges. Design: We performed a phase II trial involving patients with GCPM treated with ICB (sintilimab) combined with chemotherapy. The samples of primary tumours, GCPMs and peripheral blood from patients were collected for single-cell sequencing to comprehensively interpret the tumour microenvironment of GCPM and its impacts on immunotherapy efficacy. Results: The GCPM ecosystem coordinates a unique immunosuppressive pattern distinct from that of primary GC, which is dominated by a stroma-myeloid niche composed of SPP1+tumour-associated macrophages (TAMs) and Thrombospondin 2 (THBS2)+matrix cancer-associated fibroblasts (mCAFs). Consequently, this stroma-myeloid crosstalk is the major mediator of ICB resistance in patients with GCPM. Mechanistically, the accumulated THBS2+mCAFs facilitate the recruitment of peritoneum-specific tissue-resident macrophages and their transformation into SPP1+TAMs via the complement C3 and its receptor C3a receptor 1 (C3AR1), thereby forming a protumoral stroma-myeloid niche. Blocking the C3-C3AR1 axis disrupts the stroma-myeloid crosstalk and thereby significantly improves the benefits of ICB in in vivo models. Conclusion: Our findings provide a new molecular portrait of cell compositions associated with ICB resistance in patients with GCPM and aid in the prioritisation of therapeutic candidates to potentiate immunotherapy.

Background: Circulating tumor DNA (ctDNA) is a promising biomarker for predicting relapse in multiple solid cancers. However, the predictive value of ctDNA for disease recurrence remains indefinite in locoregional gastric cancer (GC). Here, we aimed to evaluate the predictive value of ctDNA in this context. Methods: From 2016 to 2019, 100 patients with stage II/III resectable GC were recruited in this prospective cohort study (NCT02887612). Primary tumors were collected during surgical resection, and plasma samples were collected perioperatively and within 3 months after adjuvant chemotherapy (ACT). Somatic variants were captured via a targeted sequencing panel of 425 cancer‐related genes. The plasma was defined as ctDNA‐positive only if one or more variants detected in the plasma were presented in at least 2% of the primary tumors. Results: Compared with ctDNA‐negative patients, patients with positive postoperative ctDNA had moderately higher risk of recurrence [hazard ratio (HR) = 2.74, 95% confidence interval (CI) = 1.37–5.48; P = 0.003], while patients with positive post‐ACT ctDNA showed remarkably higher risk (HR = 14.99, 95% CI = 3.08‐72.96; P < 0.001). Multivariate analyses indicated that both postoperative and post‐ACT ctDNA positivity were independent predictors of recurrence‐free survival (RFS). Moreover, post‐ACT ctDNA achieved better predictive performance (sensitivity, 77.8%; specificity, 90.6%) than both postoperative ctDNA and serial cancer antigen. A comprehensive model incorporating ctDNA for recurrence risk prediction showed a higher C‐index (0.78; 95% CI = 0.71–0.84) than the model without ctDNA (0.71; 95% CI = 0.64–0.79; P = 0.009). Conclusions: Residual ctDNA after ACT effectively predicts high recurrence risk in stage II/III GC, and the combination of tissue‐based and circulating tumor features could achieve better risk prediction.

This prospective, nonrandomized, open-label phase 2 trial (Chinese Clinical Trial Registry, ChiCTR2200061906) aimed to evaluate the effectiveness of adding the PD-1 antibody tislelizumab to perioperative chemotherapy in patients with locally advanced gastroesophageal junction adenocarcinoma (GEJA). This study enrolled patients with GEJA clinically staged as cT3-4aNanyM0 or cT1-2N+M0 from October 2022 to June 2023. Eligible patients were administered three preoperative and five postoperative 3-week cycles of treatment with PD-1 antibody tislelizumab plus SOX (S-1 and oxaliplatin) regimen. The primary endpoint was major pathological response (MPR) rate. Thirty-two patients were enrolled. The median age was 60 years (range: 28–74 years), and 53.1% (17/32) patients were Siewert III type. All patients received at least one cycle of assigned preoperative treatment, and 93.8% (30/32) patients completed three cycles of assigned preoperative tislelizumab and SOX. The R0 resection rate was 96.9% (31/32). MPR, pathological complete response (pCR) of primary tumors and ypT0N0 rates were 50.0% (16/32, 95% CI: 31.9–68.1%), 28.1% (9/32, 95% CI: 13.7–46.7%) and 25.0% (8/32, 95% CI: 11.5–43.4%), respectively. The surgical morbidity rate was 15.6% (5/32), and no 30-day mortality was observed. In the preoperative and postoperative treatment periods, the rate of treatment-related grade 3–4 adverse events was 31.2% (10/32). At the date of 7^th Jan 2025, 8 (25.0%) patients occurred recurrence. Therefore, perioperative tislelizumab plus chemotherapy demonstrated significantly improved pathological regression and might be a promising option for patients with locally advanced resectable GEJA.

Importance: Whether anti–Helicobacter pylori treatment can provide survival benefits for patients with gastric cancer who are diagnosed with H pylori infection is an area with limited research.Objective: To explore the potential survival benefits of anti–H pylori treatment after radical gastrectomy in patients with gastric cancer and presurgical confirmation of H pylori infection.Design, Setting, and Participants: This retrospective cohort study was conducted using data from patients with gastric cancer treated between January 1, 2010, and December 31, 2018, and followed up for outcome ascertainment until May 19, 2021. Propensity score matching was performed in patients treated with or without anti–H pylori treatment. This study involved a single institute in a comprehensive cancer treatment and research center located in Guangzhou, Guangdong Province, China. The study included patients with gastric or esophagogastric junction adenocarcinoma who underwent curative gastrectomy with D2 lymphadenectomy and tested positive for H pylori infection. Data were analyzed from March to June 2023.Exposure: Anti–H pylori treatment, which primarily includes triple therapy regimens consisting of amoxicillin, clarithromycin, and omeprazole for 14 days.Main Outcomes and Measures: Clinical outcomes, including overall survival (OS) and disease-free survival (DFS), were analyzed by Kaplan-Meier method, log-rank test, and Cox proportional hazards regression model. Subgroup analysis based on crucial clinical information was also conducted.Results: All 1293 patients (median [IQR] age, 59 [50-65] years; 860 [66.5%] male) were divided into 2 groups, with 125 patients in the anti–H pylori treatment group and 1168 patients in the non–anti–H pylori treatment group based on whether they received anti–H pylori treatment during the perioperative period and the follow-up. Survival analysis showed that the 5-year OS rates were 94.1% (95% CI, 89.3%-99.2%) in the anti–H pylori group and 73.8% (95% CI, 70.7%-77.0%) in the non–anti–H pylori group, and the hazard ratio (HR) of these 2 groups was 0.33 (95% CI, 0.18-0.60; P < .001). The survival benefit remained after propensity score matching (HR, 0.50; 95% CI, 0.26-0.99; P = .048). Multivariable analysis for OS and DFS further showed the survival benefit of anti–H pylori treatment, with HRs of 0.38 (95% CI, 0.17-0.87; P = .02) and 0.48 (95% CI, 0.28-0.83; P = .008), respectively. Among patients with TNM stage II/III disease who received adjuvant chemotherapy, anti–H pylori treatment was associated with survival benefits (OS: HR, 0.49; 95% CI, 0.24-0.99; P = .046), whereas among those who did not receive adjuvant chemotherapy, anti–H pylori treatment was not associated with survival benefits (OS: HR, 0.29; 95% CI, 0.04-2.08; P = .22).Conclusions and Relevance: This cohort study indicates that anti–H pylori treatment may be associated with improved survival in patients with gastric cancer who have H pylori infections. The study reinforces the importance of including H pylori screening and treatment in the surgical treatment of these patients.