In this phase 2 trial (NCT04744649), 17 patients with locally advanced Epstein-Barr virus-associated gastric or gastroesophageal junction adenocarcinoma (cT2-4aN1-3M0) received four cycles neoadjuvant toripalimab plus capecitabine/oxaliplatin. The primary endpoint was major pathological response; secondary endpoints included pathological complete response, R0 resection, adverse events, event-free survival, overall survival, and tumor microenvironment. Paired pre-/post-treatment tissues were assessed by immunofluorescence. 16 patients underwent curative resection; 1 declined surgery. Major pathological response, pathological complete response, and ypN0 were 37.5% (6/16, 95% CI 0.15-0.65), 25.0% (4/16, 95% CI 0.07-0.52), and 81.3% (13/16, 95% CI 0.54-0.96), respectively. Major pathological response was more frequent in patients with programmed death ligand 1 ≥20 (57.1%, 95%CI 0.18-0.90). Major pathological response was associated with higher pretreatment CD8⁺ T-cell density. 35.3% reported grade 3-4 adverse events. These findings suggest that neoadjuvant immunochemotherapy demonstrated favorable efficacy with a manageable safety profile in Epstein-Barr virus-associated gastric or gastroesophageal junction adenocarcinoma.

The optimal follow-up strategy for patients with locally advanced gastric cancer (LAGC) receiving neoadjuvant therapy (NAT) remains unknown. Traditional follow-up strategies based on relatively fixed intervals fail to fully account for dynamic changes in recurrence risk. This study aimed to develop a personalized postoperative follow-up strategy using dynamic programming (DP) to optimize follow-up arrangements based on individual patient characteristics and dynamic recurrence risks. This study included 3397 patients with LAGC who underwent surgery after NAT at 21 medical centers between 2018 and 2023. By integrating multiple prognostic indicators using a random survival forest model, we estimated individual time-adjusted cumulative hazards. A conditional inference tree was then used to stratify patients into low-, medium-, and high-risk groups. The DP algorithm was employed to determine the optimal follow-up arrangements for recurrence detection. A Markov decision-analytic model was used to identify the most cost-effective follow-up strategy. Compared with the guideline strategies, the DP-based strategy significantly reduced the average delayed detection time, particularly in the high-risk group. Furthermore, the cost-effectiveness analysis showed that the DP-based strategy achieved the best incremental cost-effectiveness ratio. Finally, we determined that the optimal numbers of follow-ups for the low-, medium-, and high-risk groups were 9, 10, and 13, respectively. The study demonstrates that the DP-based personalized follow-up strategy significantly improved the efficiency of recurrence detection and resource utilization in LAGC. These findings highlight the potential of DP algorithms in clinical decision-making and provide a foundation for future personalized follow-up studies.

Although neoadjuvant immunochemotherapy (nICT) improves gastric cancer (GC) outcomes, resistance remains a challenge, highlighting the need for better patient selection and strategies to overcome resistance. Here, we analyze 110 patients with GC before and after nICT or chemotherapy (nCT) from the NEOSUMMIT-01 trial using multi-omic sequencing followed by functional validation. We identify five tumor microenvironment ecotypes (EC1-5) linked to therapy. nICT achieves response in EC1 (T cell activation), EC2 (tertiary lymphoid structures), and EC3 (vascular normalization), but not in EC4 (extracellular matrix organization) and EC5 (immunosuppressive macrophage enrichment). Notably, nICT resistance in EC5 is mediated by the interaction between APOA1+ tumor cells and TREM2+ macrophages. Additionally, we reveal multiple biomarkers associated with nICT efficacy, including SBS19, HLA-B∗15:02, FDXR expression, and FGFR pathway activity, and provide a multi-omic stratification model for treatment response-based patient stratification. This study provides mechanistic insights into nICT in GC, informs therapeutic decisions, and reveals potential targets.

4079 Background: Borrmann type IV (Borrmann-IV) gastric cancer (GC), or linitis plastica, is marked by diffuse infiltration, early metastasis, and poor prognosis, with limited benefit from conventional therapies. This study evaluated the efficacy and safety of a total neoadjuvant regimen combining immunotherapy and chemotherapy in Borrmann-IV GC. Methods: This trial (NCT06451211) enrolled patients with Borrmagnn-IV gastric cancer without distant metastasis. Participants received a total neoadjuvant regimen consisting of tislelizumab (an anti–PD-1 antibody) combined with platinum-based chemotherapy (oxaliplatin plus capecitabine or S-1) for 6 cycles at 3-week intervals, followed by radical surgical resection. The prespecified primary endpoint was the pathological response rate, defined as tumor regression grade (TRG) 0/1. Results: A total of 56 patients were enrolled, all patients had no distant metastasis confirmed by laparoscopic exploration and ascitic fluid cytology. The median age was 58 years; all patients were pMMR. In the efficacy analysis population (n=47), 41 patients completed 5–6 cycles and 6 patients completed 3–4 cycles of preoperative chemotherapy plus immunotherapy, no patients experienced disease progression leading to tumor metastasis during preoperative treatment. 47 patients underwent radical surgical resection, including 42 total gastrectomy, with an R0 resection rate of 98% (46/47). The prespecified primary endpoint of TRG 0/1 was achieved in 32% of patients (15/47; 95% CI, 21%–48%). Notably, 17% (n = 8) achieved pCR (ypT0N0), and 53% (n =25) were ypN0. Pathological response (TRG 0/1) was significantly higher in Lauren intestinal/mixed versus diffuse types (53% vs. 21%; p < 0.05), while efficacy was comparable between PD-L1 CPS ≥5 and <5 (44% vs. 30%). Grade 3/4 treatment-related adverse events occurred in 32% of patients (n=18), mainly thrombocytopenia and liver function impairment. Surgical morbidity (Clavien–Dindo grade II/III) occurred in 10.6% of surgical patients (5/47), including 1 patient with postoperative bleeding and 3 patients with anastomotic leakage; no perioperative mortality was observed. Conclusions: Total neoadjuvant tislelizumab plus chemotherapy demonstrated promising efficacy and an acceptable safety profile in patients with Borrmann-IV gastric cancer. Lauren classification may serve as a potential predictive biomarker and warrants further study. Clinical trial information: NCT06451211 .

The NEOSUMMIT-01 trial previously showed that adding the PD-1 antibody toripalimab to perioperative chemotherapy improved the pathologic response in patients with locally advanced gastric or gastroesophageal junction cancer. Here, we present the event-free survival (EFS) and overall survival (OS) after extended follow-up. A total of 108 patients were enrolled (toripalimab plus chemotherapy, n = 54; chemotherapy alone, n = 54). At the data cutoff date (August 29, 2025), the median follow-up was 43.2 months (interquartile range: 36.6-53.7). The 3-year EFS was 74.7% (95% CI, 63.6% to 87.7%) in the toripalimab plus chemotherapy group and 56.2% (95% CI, 43.3% to 73.0%) in the chemotherapy group, with a hazard ratio (HR) of 0.51 (95% CI, 0.27 to 0.98; P = .044). The 3-year OS was 81.3% (95% CI, 71.4% to 92.4%) versus 72.2% (95% CI, 61.2% to 85.2%), respectively, with an HR of 0.45 (95% CI, 0.21 to 0.95; P = .036). The survival benefits were consistent across most predefined subgroups and were maintained in the analysis excluding patients with dMMR. In conclusion, perioperative toripalimab plus chemotherapy significantly improved 3-year EFS and OS compared with chemotherapy alone, suggesting it as a promising treatment option for patients with locally advanced gastric or gastroesophageal junction cancer.

282 Background: The NEOSUMMIT-01 trial evaluated the efficacy of adding the PD-1 antibody toripalimab to perioperative chemotherapy in patients with locally advanced, resectable gastric or gastroesophageal junction (GEJ) cancer. Previously, we reported significant improvements in pathological complete or moderate regression (TRG 0/1) rate (44.4% vs 20.4%, P =0.009) and pathological complete response (pCR) rate (22.2% vs 7.4%, P =0.030) with the addition of toripalimab (2023 ASCO Abstract 4001; Nature Medicine 2024). Here, we present the 3-year survival outcomes after extended follow-up. Methods: In this open-label, randomized, phase 2 trial, patients with resectable gastric or GEJ cancer (clinical stage cT3–4a N+ M0) were randomized (1:1) to receive either three preoperative and five postoperative cycles of SOX/XELOX chemotherapy (chemotherapy group), or the same chemotherapy combined with toripalimab, followed by toripalimab monotherapy for 6 months (toripalimab plus chemotherapy group). The primary endpoint was pathological complete or moderate regression rate (TRG 0/1). Secondary endpoints included pathological complete response (pCR), R0 resection rate, objective response rate, disease control rate, event-free survival (EFS), overall survival (OS), and treatment safety. This analysis focuses on 3-year EFS and OS, assessed in the intention-to-treat population. The trial is registered at ClinicalTrials.gov (NCT04250948). Results: Between October 12, 2019, and June 27, 2022, 108 patients were enrolled (toripalimab plus chemotherapy, n = 54; chemotherapy alone, n = 54) and included in the intention-to-treat analysis. As of the clinical cutoff date (August 29, 2025), the median follow-up was 43.2 months (IQR 36.6–53.7). The 3-year EFS was 74.7% (95% CI: 63.6–87.7%) in the toripalimab plus chemotherapy group and 56.2% (95% CI: 43.3–73.0%) in the chemotherapy group, with a hazard ratio (HR) of 0.52 (95% CI: 0.27–1.00; P = 0.047). The 3-year OS was 81.3% (95% CI: 71.4–92.4%) versus 72.2% (95% CI: 61.2–85.2%), respectively, with an HR of 0.45 (95% CI: 0.21–0.95; P = 0.031). Conclusions: Perioperative toripalimab combined with chemotherapy demonstrated significantly improved 3-year EFS and OS compared to chemotherapy alone, suggesting it as a promising treatment option for patients with locally advanced, resectable gastric or GEJ adenocarcinoma. Clinical trial information: NCT04250948 .

BACKGROUND:Adjuvant chemotherapy following D2 gastrectomy constitutes the standard-of-care for resectable gastric or gastroesophageal junction (GEJ) carcinoma. The CAPITAL trial is a multicenter, randomized, phase 3 study, aiming to assess the efficacy and safety of adjuvant oxaliplatin plus S-1 (SOX) versus S-1 alone. METHODS:Patients with histologically confirmed pathological stage II-III gastric or GEJ adenocarcinoma after gastrectomy with D2 lymphadenectomy were randomly assigned (1:1) to receive either the SOX regimen (n = 362) or the S-1 regimen (n = 362). The primary endpoint was overall survival. This study is registered with ClinicalTrials.gov (NCT01795027). FINDINGS:The median follow-up was 74.0 months (interquartile range [IQR], 35.5-89.3). The 5-year overall survival rates were 70.9% (95% confidence interval [CI], 66.0-76.1) in the SOX group and 62.9% (95% CI, 57.8-68.5) in the S-1 group (hazard ratio [HR], 0.74; 95% CI, 0.58-0.95; p = 0.018). The 3- and 5-year disease-free survival rates were 71.2% (95% CI, 66.5-76.3) and 66.2% (95% CI, 61.2-71.6) in the SOX group, as compared with 65.1% (95% CI, 60.2-70.5) and 55.6% (95% CI, 50.4-61.3) in the S-1 group (HR, 0.76; 95% CI, 0.61-0.96). Treatment-related adverse events of grade 3-4 occurred in 87 (25%) of 349 patients in the SOX group and 45 (13%) of 347 patients in the S-1 group. The most common grade 3-4 adverse event was neutropenia, occurring in 44 (13%) of 349 patients in the SOX group and 23 (7%) of 347 patients in the S-1 group. CONCLUSIONS:The addition of adjuvant oxaliplatin to S-1 chemotherapy significantly improved overall survival and disease-free survival in patients with gastric cancer. FUNDING:This research was supported by the National Natural Science Foundation of China (82573092 and 82573387).

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.

Figure S5: 293T cells were transfected with Myc-TRIM50 plasmid, Flag-JUP plasmid and HA-Ub plasmid, whole-cell lysates were subjected to SDS denaturation and immunoprecipitation with JUP antibody and immunoblot analysis with the indicated antibodies.

e16108 Background: Treatment options for Borrmann Type 4 gastric cancer (Linitis Plastica) have long been a topic of debate. This patient group is characterized by diffuse cancer infiltration throughout the stomach, early metastasis, and a poor prognosis. In this study, we aim to evaluate the efficacy and safety of combining immunotherapy with chemotherapy for patients with Borrmann Type 4 (B-IV) or large Type 3 (B-III) gastric cancer. Methods: Patients (pts) diagnosed with gastric adenocarcinoma (B-IV or B-III) without distant metastasis were eligible for the study. Participants received a prolonged neoadjuvant treatment regimen consisting of the anti-PD-1 inhibitor (ICI) Tislelizumab and platinum-based chemotherapy (oxaliplatin combined with either capecitabine or S-1) administered in 3-week cycles. After completing six cycles, patients underwent radical surgery. The primary endpoint was the pathological response rate, assessed using the tumor regression grade (TRG) system. Results: As of January 2025, 42 pts were enrolled in this trial (intention-to-treat group), of whom 27 completed the neoadjuvant treatment and underwent radical gastrectomy. Among the 27 pts, 17 completed all the 6 cycles of neoadjuvant treatment, while 5 pts completed either 3-4 cycles or 5 cycles. All 42 pts were included in the safety and demographics analysis, while 27 were included in the efficacy analysis. The median age was 59 (range: 31–73), with 57% male. All pts had an ECOG performance status of 0 or 1, and 79% (33 pts) were B-IV. Lauren’s histological classification included intestinal (12 pts), diffuse (18 pts), and mixed (9 pts) types. 38 pts showed proficient mismatch repair proteins(pMMR, the other 4 not evaluated). Following surgery, all 27 pts had R0 resection. 11 of 27 pts (41%) demonstrated a pathological response of TRG 0/1 (95% CI: 24%–59%), exceeding the prespecified endpoint. Pts with a PD-L1 CPS score ≥5 or < 5 showed a comparable percentage of those with TRG 0/1. Notably, 7 pts (26%) achieved ypTNM stage 0 (pCR), and 18 pts (67%) were ypN0. A significantly higher pathological response rate (TRG 0/1) was observed in pts with Lauren’s intestinal or mixed types (9/16, 59%; 95% CI: 36%–78%) compared to those with diffuse type (2/11, 18%; 95% CI: 3%–48%; p < 0.05). Treatment-related adverse events were reported in 35 of 42 pts (83%), with common events including thrombocytopenia, nausea, and liver injury. 7 pts (17%) experienced grade 3/4 adverse events. 5 pts (18%) underwent surgical morbidity including bleeding, anastomotic leak and infection. Conclusions: Prolonged neoadjuvant treatment with ICI Tislelizumab combined with platinum-based chemotherapy demonstrated promising clinical efficacy and a manageable safety profile in pts with B-IV or large B-III gastric cancer. The study is ongoing and up to 53 pts will be enrolled into this cohort. Clinical trial information: NCT06451211 .

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 7th 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.

Advanced gastric cancer (GC) exhibits a high recurrence rate and a dismal prognosis. Myocyte enhancer factor 2c (MEF2C) was found to contribute to the development of various types of cancer. Therefore, our aim is to develop a prognostic model that predicts the prognosis of GC patients and initially explore the role of MEF2C in immunotherapy for GC. Transcriptome sequence data of GC was obtained from The Cancer Genome Atlas (TCGA), the Gene Expression Omnibus (GEO) and PRJEB25780 cohort for subsequent immune infiltration analysis, immune microenvironment analysis, consensus clustering analysis and feature selection for definition and classification of gene M and N. Principal component analysis (PCA) modeling was performed based on gene M and N for the calculation of immune checkpoint inhibitor (ICI) Score. Then, a Nomogram was constructed and evaluated for predicting the prognosis of GC patients, based on univariate and multivariate Cox regression. Functional enrichment analysis was performed to initially investigate the potential biological mechanisms. Through Genomics of Drug Sensitivity in Cancer (GDSC) dataset, the estimated IC50 values of several chemotherapeutic drugs were calculated. Tumor-related transcription factors (TFs) were retrieved from the Cistrome Cancer database and utilized our model to screen these TFs, and weighted correlation network analysis (WGCNA) was performed to identify transcription factors strongly associated with immunotherapy in GC. Finally, 10 patients with advanced GC were enrolled from Sun Yat-sen University Cancer Center, including paired tumor tissues, paracancerous tissues and peritoneal metastases, for preparing sequencing library, in order to perform external validation. Lower ICI Score was correlated with improved prognosis in both the training and validation cohorts. First, lower mutant-allele tumor heterogeneity (MATH) was associated with lower ICI Score, and those GC patients with lower MATH and lower ICI Score had the best prognosis. Second, regardless of the T or N staging, the low ICI Score group had significantly higher overall survival (OS) compared to the high ICI Score group. For its mechanisms, consistently, for Camptothecin, Doxorubicin, Mitomycin, Docetaxel, Cisplatin, Vinblastine, Sorafenib and Paclitaxel, all of the IC50 values were significantly lower in the low ICI Score group compared to the high ICI Score group. As a result, based on univariate and multivariate Cox regression, ICI Score was considered to be an independent prognostic factor for GC. And our Nomogram showed good agreement between predicted and actual probabilities. Based on CIBERSORT deconvolution analysis, there was difference of immune cell composition found between high and low ICI Score groups, probably affecting the efficacy of immunotherapy. Then, MEF2C, a tumor-related transcription factor, was screened out by WGCNA analysis. Higher MEF2C expression is significantly correlated with a worse OS. Moreover, its higher expression is also negatively correlated with tumor mutation burden (TMB) and microsatellite instability (MSI), but positively correlated with several immunosuppressive molecules, indicating MEF2C may exert its influence on tumor development by upregulating immunosuppressive molecules. Finally, based on transcriptome sequencing data on 10 paired tumor tissues from Sun Yat-sen University Cancer Center, MEF2C expression was significantly lower in paracancerous tissues compared to tumor tissues and peritoneal metastases, and it was also lower in tumor tissues compared to peritoneal metastases, indicating a potential positive association between MEF2C expression and tumor invasiveness. Our prognostic model can effectively predict outcomes and facilitate stratification GC patients, offering valuable insights for clinical decision-making. The identified transcription factor MEF2C can serve as a biomarker for assessing the efficacy of immunotherapy for GC.

Figure S4: The TRIM50 and JUP binding domain predicted by I-TASSER-MTD. Blue indicated TRIM50. Green indicated JUP. Purple highlighted the interaction sites in RING and PRY/SPRY domain.

Figure S7: TOPFLASH analysis of JUP in TRIM50 overexpressing versus control empty vector 293T cells.

4069 Background: Surgery remains the cornerstone of curative therapy for locally advanced GC/EGJC. EBV-positive tumor is a distinct molecular subtype that would be potentially sensitive to immunotherapy, but no consistent reports. Given that chemotherapy may enhance antitumor immunity, perioperative immunochemotherapy may be a promising modality for EBV-positive patients. Methods: The NICE trial is a multicenter, multi-cohort phase II study (NCT04744649) evaluating the safety and efficacy of toripalimab plus CapeOX as perioperative treatment in patients with locally advanced GC/EGJC. The Cohort B was first of its kind to assess the efficacy of the immunochemotherapy on the EBV-positive GC/EGJC , in which patients received toripalimab (240 mg) combined with standard-dose CapeOX every 3 weeks for 4 cycles preoperatively and 4 cycles postoperatively. Eligibility criteria included clinical tumor stages of cT3-4aNxM0 or cT2N+M0 disease as determined by both imaging scan and staging laparoscopy with negative peritoneal cytology. The primary endpoint was major pathologic response (MPR, defined as < 10% viable tumor cells). The tumor immune microenvironment (TIME) of tissue samples obtained before and after treatment was analyzed using multiple immunofluorescence assays to assess changes in immune cell infiltration and other biomarkers related to treatment response. Results: From May 2021 to September 2023, 17 patients with EBV-positive GC/EGJC (GC, n = 15; EGJC, n = 2) were enrolled, with cT2N0 (n = 1), cT3N1-3 (n = 5), and cT4aN1-3 (n = 11). All patients completed 4 preoperative cycles of treatment, and none experienced progression before surgery. Only one patient withdrew the inform content after preoperative therapy, the 16 patients underwent radical resection, achieving a 100% R0 resection rate (16/16). The MPR rate was 37.5% (6/16), and pathological complete response rate (pCR) was 25.0% (4/16). Of the 16 participants, 15 received postoperative adjuvant therapy, while 1 declined further treatment. The TIME analysis results showed that tumor-infiltrating CD8+ T cells in post-treatment tumor tissues significantly clonally expanded compared with pre-treatment paired tissues. Treatment-related grade 3/4 adverse events were observed in 6 patients (35.3%, 6/17). Until Dec 31 2024, none of the patients experienced disease recurrence. Conclusions: Neoadjuvant toripalimab combined with CapeOX is a safe and effective treatment option for patients with EBV-positive, locally advanced GC/EGJC, with moderate MPR and pCR, indicating further investigating for this distinct type of cancer. Clinical trial information: NCT04744649 .

Figure S3A: Tumor photograph in the nude mouse subcutaneous xenograft model by implanting TRIM50 overexpressing (TRIM50) versus control empty vector (EV) MKN45 cells (n = 6 mice per group). Scale bar: 1 cm Figure S3B: MKN74 cells were transfected with lentiviruses expressing TRIM50 shRNA. A universal nonsilencing shRNA was used as a negative control (sh-NC). Whole-cell lysates were subjected to immunoblot analysis with TRIM50 antibody. Figure S3C: Tumor photograph in the nude mouse subcutaneous xenograft model by implanting TRIM50 knockdown (TRIM50 sh-1/TRIM50 sh-2) versus control (TRIM50 sh-NC) MKN74 cells (n = 6 mice per group). Scale bar: 1 cm

Supplementary Tables 1-2, Supplementary Figures 1-7

The use of trastuzumab and programmed death-1 (PD-1) inhibitor is effective in patients with HER2-positive advanced gastric or gastro-esophageal junction cancer; however, their use has not been investigated in patients with localized disease. This phase 2 trial evaluates the safety and efficacy of dual PD-1 (sintilimab) and HER2 blockade with chemotherapy in patients with resectable HER2-positive gastric and gastro-esophageal junction adenocarcinoma. 22 patients are enrolled, and 20 patients undergo surgery. The primary endpoint is achieved; 12 (55%, 95% confidence interval [CI]: 32-76) of 22 patients have a major pathological response, and 11 (50%, 95% CI: 28-72) of 22 patients achieve pathological complete response. The most common grade 3 treatment-related adverse events are neutropenia and thrombocytopenia. No treatment-related deaths occur. Transcriptomic analysis, bioinformatics analysis, and immunofluorescence staining demonstrate that regulatory T cells are associated with possibility of drug resistance. This study was registered at the Chinese Clinical Trial Registry (identifier: ChiCTR2200058732).

Figure S2: Immunoblotting assay of TRIM50 expression in GC cells.