Gastric cancer treatment: recent progress and future perspectives

The assessment of human epidermal growth factor receptor 2 (HER2), microsatellite instability (MSI) and programmed cell death-ligand 1 (PD-L1) expression is relevant for the selection and effectiveness of targeted therapy in gastric cancer (GC). We aimed to investigate the clinicopathological characteristics and prognosis of GC patients according to these profiles. GC patients who underwent gastrectomy with D2 lymphadenectomy were eligible. HER2, MSI status and PD-L1 expression were analyzed by immunohistochemistry (IHC). Patients were grouped as follows: HER2+ group, immunotherapy (IT) group (MSI and/or PD-L1+), and non-targeted therapy (NTT) group (stable microsatellite and HER2/PD-L1-). Among 282 patients, 50 (17.7%) were HER2+ and 79 (28%) MSI/PD-L1+. Fifteen had HER2+ and MSI/PD-L1+, while 168 (59.6%) were in the NTT group. HER2+ GCs were related to male gender (p = 0.007), intestinal type (p = 0.001) and less advanced pTNM stage (p = 0.029). Older age (p = 0.003), subtotal gastrectomy (p = 0.025), intestinal type (p = 0.008), pN0 status (p = 0.002) and less advanced pTNM stage (p = 0.001) were associated with the IT group. IT GC had better disease-free survival (DFS) and overall survival than the NTT group (p = 0.015 and p = 0.027, respectively). Concerning patients eligible for the standard adjuvant therapy, the treatment impacted positively on DFS for HER2+ and NTT groups (p = 0.003 and p = 0.042, respectively). No difference in DFS was seen between IT patients who received perioperative/adjuvant therapy and those treated only with surgery (p = 0.160). GC patients who exhibited markers that can serve as an indication for known targeted therapy represent 40.4% of cases. The IT group was associated with a better prognosis. No benefit with standard adjuvant treatment appears to be achieved in MSI/PD-L1+ GCs.

e15609 Background: Recent data supports a potentially significant role for immune checkpoint inhibitors in the treatment of gastric cancer. However, there are few data on the clinical implications of immunotherapy markers in gastric signet-ring cell carcinoma (SRCC). We evaluated the expression of programmed cell death protein-1 (PD-1), programmed cell death ligand 1 (PD-L1), infiltration by CD3+ T cell, microsatellite instability (MSI), and Epstein-Barr Virus (EBV), and the relationship of each factor to survival in SRCC patients. Methods: SRCC samples from 89 patients were stained by immunohistochemistry to evaluate PD-L1, PD-1, CD3+ T cells, and MSI. EBV was detected by DNA in-situ hybridization. Results: All 89 patients had advanced gastric SRCC (89.9% were stage III, 10.1% were stage IV). All patients received 5-FU-based first-line chemotherapy. PD-L1 and PD-1 were expressed in 40.4% and 18.0% of the patients, respectively. There was a significant correlation between PD-L1 and PD-1 expression (r = 0.363, p < 0.001). There was loss of at least 1 of the 4 DNA mismatch repair (DNA-MMR) gene proteins in 32.6% of samples. However, there was no association between the expression of PD-L1, PD-1 or MSI status to overall survival (OS). Only 1 case out of 89 was EBV positive, with concurrent PD-L1 positivity, a high degree of CD3+ T cell infiltration and MSI. Increased CD3+ T cells numbers was associated with increased PD-1 expression (r = 0.256, p = 0.012) and MSI status (r = 0.208, p = 0.05). High CD3+ T cell infiltration was related to better OS (23.7 months, 95% CI: 19.0-38.0 vs 15.8 months, 95% CI: 13.0-22.0, p = 0.033), but was not an independent prognostic factor for survival after multivariate analysis (HR = 0.68, 95% CI: 0.42-1.10, p = 0.116). Conclusions: CD3+ T cell was more infiltrated in PD-1 positive, tumors with MSI and were associated with better OS, indicating an adaptive immune resistance may be occurring. Further research into the cancer characteristics and immunotherapy markers of the gastric SRCC immune microenvironment may highlight targets for immunotherapy.

The National Comprehensive Cancer Network (NCCN) issued the clinical practice guidelines for gastric cancer 2017 edition version 5, which has been fully updated for the treatment of gastric cancer, including systematic treatment, surgery and radiotherapy. This article review and summarize the updated NCCN clinical practice guidelines for gastric cancer in 2017 and try to interpret it. (1)Biomarkers: mismatch repair defect (dMMR) or high microsatellite instability (MSI-H), programmed death ligand 1 (PD-L1) and tumor Epstein Barr virus (EBV) status should be considered for patients with gastric cancer. (2)Treatment of advanced gastric cancer: the major update is the application of immunotherapy (Pembrolizumab, Nivolumab combined with Ipilimumab). (3)Adjuvant therapy after D2 resection and perioperative treatment: the guidelines recommended Capecitabine combined with Oxaliplatin as adjuvant therapy after radical operation, updated from category 2A to 1; although the 2017 edition of the NCCN guidelines have not yet been adopted, Docetaxel-based FLOT scheme has certain potential in adjuvant therapy for gastric cancer. (4) Radiotherapy: a more detailed definition of radiotherapy for gastric cancer in different locations, especially in high-risk lymphatic drainage areas, was updated. (5) Genetic risk assessment: the guidelines recommended genetic screening for gastric cancer, including hereditary diffuse gastric cancer (HDGC), Lynch syndrome, juvenile polyposis (JPS), Peutz-Jephers syndrome (PJS) and familial adenomatous polyposis (FAP). The NCCN guidelines continue to update based on new evidences, which is the embodiment of precision medicine in the treatment of gastric cancer. The biggest change in the 2017 gastric cancer guidelines is the updates of immunotherapy, which also suggests that the direction of the gastric cancer treatment began to turn to immunotherapy.

Globally, 968 350 new cases and 659 853 deaths from gastric cancer were reported in 2022. In the US, 30 300 new cases and 10 780 deaths were estimated in 2025. Gastric cancer is more common in men, and the median age at diagnosis is 68 years. Most gastric cancers (>90%) are adenocarcinomas. Worldwide, 85% of cases arise from the stomach body or antrum and 15% from the cardia. In the US, more than 90% of patients diagnosed with gastric cancer present with symptoms such as weight loss and abdominal pain. At presentation, approximately 13% have localized disease (limited to the stomach), 15% to 25% have locally advanced disease, defined as a tumor that has spread to regional lymph nodes, and 35% to 65% have metastatic disease. Helicobacter pylori infection is a treatable risk factor associated with 90% of gastric body and antrum cancers globally. Additional modifiable risk factors include smoking, alcohol, obesity, and salt intake. In countries with high incidence such as Japan and Korea, routine endoscopic screening beginning at age 40 years is associated with improved survival. Diagnosis is made by endoscopic biopsy. Patients with localized gastric cancer are treated with surgical resection and have a 5-year relative survival rate of 75% with treatment. Patients with more advanced-stage disease should receive gastrectomy, perioperative chemotherapy with 5-fluorouracil, oxaliplatin, and docetaxel and immunotherapy (durvalumab). Metastatic or unresectable disease may be treated with chemotherapy, immunotherapy, and/or targeted therapy depending on biomarkers, including programmed cell death ligand 1 (PD-L1), human epidermal growth factor receptor 2 (ERBB2; formerly HER2 or HER2/neu), and claudin-18, isoform 2 (CLDN18.2). For PD-L1-expressing gastric cancer, adding immune checkpoint inhibitors, such as nivolumab and pembrolizumab, is associated with an additional 3 months of survival when compared with chemotherapy alone. For gastric cancers overexpressing the ERBB2 or CLDN18.2 proteins, the addition of trastuzumab or zolbetuximab, respectively, is associated with an additional 3 to 4 months' survival. Early supportive care focusing on symptom management and on nutritional and psychosocial support is associated with 3 months of survival benefit. Less than 10% of patients with metastatic gastric cancer survive more than 5 years. Approximately 30 300 new cases of gastric cancer are diagnosed annually in the US. Localized gastric cancer is treated with gastrectomy, and locally advanced disease is treated with surgery and chemoimmunotherapy. For patients with unresectable or metastatic gastric cancer, chemotherapy with immune checkpoint inhibitors and targeted therapies such as trastuzumab or zolbetuximab improves survival by several months.

Background: Gastric cancer (GC) is one of the most lethal cancers worldwide. Although GC was historically considered a single entity within the organ of origin, nowadays it is acknowledged that GC represents a heterogeneous disease. Nevertheless, in this field there is still a lack of biomarkers able to guide the choice of the best treatment options for each patient. This review aims to summarize the prognostic and predictive biomarkers evaluated in GC and their role as a guide for treatment for precision medicine. Summary: Human epidermal growth factor receptor 2 overexpression represents the only predictive molecular biomarker validated in GC, while its prognostic role is still controversial. Microsatellite instability and Epstein-Barr virus status are promising for prediction of the response to immunotherapy. The role of other biomarkers (ctDNA, programmed death ligand 1 [PD-L1], and TMB), as well as the practical application of molecular classifications, requires further evaluation before use in clinical practice. 18-FDG-PET scan could be useful as a predictive tool in non-metastatic GC patients receiving a perioperative approach. Finally, the tumor microenvironment may have an evolving role in the future. Key Messages: GC is a heterogeneous disease and targeted approaches are needed. The finding of prognostic and predictive factors is a hot topic in the field of GC personalized medicine.

Understanding mechanisms of primary resistance to checkpoint inhibitors will lead to precision immunotherapy of advanced gastric cancer

CXC chemokine receptor 4 (CXCR4) and programmed cell death‐ligand 1 (PD‐L1) are two critical molecules involved in the tumor immune microenvironment. However, the impact of platinum drugs, such as cisplatin, on CXCR4 or PD‐L1 expression and the underlying mechanisms in gastric cancer (GC) remain unknown. Moreover, the correlation between their expression levels in GC remains elusive. Immunohistochemistry, western blot, and RT‐qPCR were performed to determine the expression pattern of CXCR4 and PD‐L1 in GC. Clinical samples, patient‐derived xenografts, and cell‐derived xenografts were utilized to investigate the effects of platinum drugs on the expression levels of CXCR4 and PD‐L1. Postchemotherapy resected GC tumor tissues showed higher CXCR4 and PD‐L1 expression levels than pretreatment biopsies (p < 0.05). Similarly, GC xenografts treated with platinum‐based chemotherapy exhibited increased CXCR4 and PD‐L1 expression levels compared to saline‐treated controls (p < 0.05). A positive correlation was detected between the expression levels of CXCR4 and PD‐L1 in GC tumor tissues. Increased levels of CXCR4 and PD‐L1 expression, in a dose‐ and time‐dependent manner upon cisplatin treatment, were observed in GC cells (p < 0.05). Cisplatin‐induced CXCR4 upregulation relies on ROS/HIF‐1α and ROS/NF‐κB pathways, while cisplatin‐induced PD‐L1 upregulation is cyclic GMP‐AMP synthase/stimulator of IFN genes‐dependent and associated with elevated ROS levels in GC cells. CXCR4 expression was found to be positively correlated with PD‐L1 expression in GC. Platinum drugs upregulated the levels of CXCR4 and PD‐L1 expression in GC. A combined strategy targeting CXCR‐4 and PD‐L1 might have clinical prospects for GC patients.

Introduction. Perioperative FLOT chemotherapy has improved prognosis in patients with locally advanced resectable gastric cancer (GC). However, in 80 % of cases, the tumor is resistant to the therapy, resulting in unnecessary toxicity and delayed surgical treatment.Aim. Evaluation of clinico-morphological patterns of microsatellite instability, HER2 gene amplification, changes in gene copy number and their relationship with the response to perioperative FLOT chemotherapy in patients with locally advanced resectable GC.Materials and methods. The retrospective study included 185 patients. All tumor samples were assessed for HER2 and microsatellite instability status. Among all cases there were 45 patients with locally advanced T2–4N1–2 M0 GC, who underwent a total or subtotal gastrectomy with D2 lymphadenectomy and perioperative chemotherapy with FLOT. Microsatellite instability detection was performed using fragment analysis, HER2 gene amplification testing – fluorescent in situ hybridization. Also 19 patients were tested for copy number changes of the FGFR1, FGFR2, KRAS, MET, EGFR, CCND1, MYC genes using Multiplex ligation-dependent probe amplification. The endpoints were progression-free survival and objective response rate.Results. Microsatellite instability was detected in 4.8 % (9/185) of GC cases. Microsatellite instability was associated with advanced age (p = 0.005), low grade of differentiation (p = 0.011), presence of tumor-infiltrating lymphocytes (p = 0.0004), and high preoperative CA 72–4 levels (p = 0.025). Prevalence of HER2 amplification was 7.5 % (14/185). It was associated with low grade of differentiation (p = 0.048) and metastasis in regional lymph nodes (p = 0.037). PFS in patients with HER2-positive (HER2 – human epidermal growth factor receptor 2) GC treated with perioperative FLOT chemotherapy (4/45) was significantly lower than in patients with HER2-negative GC: the median was 156 and 317 days, respectively (hazard ratio 0.49; 95 % confidence interval 0.16–1.47; p = 0.0006). There was no correlation between the presence of the alteration and ORR (p = 1.0). Progression-free survival in GC patients with KRAS amplification (3/19) was significantly lower comparing with patients without it: the median was 98 and 327 days, respectively (hazard ratio 0.29; 95 % confidence interval 0.07–1.19; p 0.0001). There was no association between an increase in KRAS copy number and objective response rate (p = 1.0). For microsatellite instability and other studied markers no statistically significant correlation with progression-free survival and objective response rate was found (p 0.05).Conclusion. The presence of HER2 and KRAS amplification have been shown as promising predictive markers of the treatment failure in patients treated with perioperative FLOT chemotherapy for locally advanced resectable GC.

Simple SummaryHER2 may contribute to immune evasion in gastric cancer that is associated with PD-L1 expression. Autologous organoid/immune cell co-cultures serve as an appropriate in vitro model to study the effects of anti-HER2 targeted therapy in combination with anti-PD1 immune checkpoint inhibition and may be used as an ex vivo tool for precision medicine.(1) Background: The expression of programmed death-ligand 1 (PD-L1), which interacts with programmed cell death protein 1 (PD-1) on cytotoxic T lymphocytes (CTLs), enables tumors to escape immunosurveillance. The PD-1/PD-L1 interaction results in the inhibition of CTL proliferation, and effector function, thus promoting tumor cell evasion from immunosurveillance and cancer persistence. Despite 40% of gastric cancer patients exhibiting PD-L1 expression, only a small subset of patients responds to immunotherapy. Human epidermal growth factor receptor2 (HER2) is one of the critical regulators of several solid tumors, including metastatic gastric cancer. Although half of PD-L1-positive gastric tumors co-express HER2, crosstalk between HER2 and PD-1/PD-L1 in gastric cancer remains undetermined. (2) Methods: Human gastric cancer organoids (huTGOs) were generated from biopsied or resected tissues and co-cultured with CTLs and myeloid-derived suppressor cells (MDSCs). Digital Spatial Profiling (DSP) was performed on FFPE tissue microarrays of numerous gastric cancer patients to examine the protein expression of immune markers. (3) Results: Knockdown of HER2 in PD-L1/HER2-positive huTGOs led to a concomitant decrease in PD-L1 expression. Similarly, in huTGOs/immune cell co-cultures, PD-L1 expression decreased in huTGOs and was correlated with an increase in CTL proliferation which enhanced huTGO death. Treatment with Nivolumab exhibited similar effects. However, a combinatorial treatment with Mubritinib and Nivolumab was unable to inhibit HER2 expression in co-cultures containing MDSCs. (4) Conclusions: Our study suggested that co-expression of HER2 and PD-L1 may contribute to tumor cell immune evasion. In addition, autologous organoid/immune cell co-cultures can be exploited to effectively screen responses to a combination of anti-HER2 and immunotherapy to tailor treatment for gastric cancer patients.

BackgroundThe prognostic potential of PD-L1 is currently unclear in gastric carcinomas, although the immune checkpoint PD-1/PD-L1 inhibitors have produced promising results in clinical trials.MethodsWe explored the prognostic implications of programmed death ligand 1 (PD-L1) in 514 consecutive surgically-resected gastric carcinomas. Overall survival and recurrence-free survival were evaluated. Immunohistochemistry for PD-L1, CD8, FOXP3, and PD-1, and molecular grouping by in situ hybridization for Epstein-Barr virus (EBV)-encoded small RNAs and multiplex PCR for microsatellite instability (MSI) markers were performed. Additionally, to explore the function inherent to PD-L1, PD-L1-specific siRNA transfection, cell proliferation, invasion, migration and apoptosis assays were conducted in five gastric carcinoma cell lines.ResultsPD-L1(+) tumor and immune cells were observed in 101 (20%) and 244 patients (47%), respectively. “Tumoral PD-L1(+)/immune cell PD-L1(-)/CD8+/low tumor-infiltrating lymphocytes (TILs),” and more advanced-stage tumors were associated with unfavorable clinical outcomes in the entire cohort through multivariate analysis. Furthermore, tumoral PD-L1(+)/FOXP3+/low TILs were associated with worse clinical outcomes in EBV-positive and MSI-high carcinomas. Tumoral PD-L1(+) alone was an adverse prognostic factor in EBV-positive carcinomas, but not in MSI-high carcinomas, whereas PD-L1(+) immune cells or FOXP3+/high TILs alone were correlated with a favorable prognosis. PD-L1 knockdown in gastric carcinoma cells suppressed cell proliferation, invasion and migration, and increased apoptosis, which were all statistically significant in two EBV(+) cell lines, but not all in three EBV(−) cell lines.ConclusionsThe prognostic impact of PD-L1 may depend on the tumor microenvironment, and statuses of EBV and MSI, although PD-L1 innately promotes cancer cell survival in cell-based assays. The combination of “tumoral PD-L1/immune cell PD-L1/CD8+ TILs” may serve as an independent prognostic factor. Tumoral PD-L1(+)/immune cell PD-L1(−)/CD8+/low TILs showing a worse prognosis may be beneficial for combinatorial therapies of anti-PD-L1/PD-1 and anti-cytotoxic T-lymphocyte associated antigen 4 (CTLA4) that would promote effector T cells, thus attack the tumor.

Gastric cancer (GC) is one of the most common malignancies. Immunotherapy is a promising targeted treatment. The immune regulatory programmed death‐1 (PD‐1)/programmed death‐ligand 1 (PD‐L1) axis has been used as a checkpoint target for immunotherapy. Currently, considerable discrepancies exist concerning the expression status of PD‐L1 and its prognostic value in GC. We aimed to evaluate the expression rates of PD‐L1 in GC, and further assess its relationship with mismatch repair (MMR), and human epidermal growth factor receptor 2 (HER2) status. We retrospectively collected 550 consecutive cases of GC in Fudan University Shanghai Cancer Center from 2010 to 2012. PD‐L1, MMR protein, and HER2 status were detected by immunohistochemistry (IHC). Fluorescence in situ hybridization was further used in HER2 IHC 2+ cases. Cases with at least 1% membranous and/or cytoplasmic PD‐L1 staining in either tumor cells (TCs) or tumor‐infiltrating immune cells (TIICs) were considered as PD‐L1 positive. The correlation between clinicopathological parameters, HER2, MMR, and PD‐L1 expression status was determined using chi‐squared tests. About 37.3% cases (205/550) showed PD‐L1 expression in TCs and/or TIICs. 17.3% cases (95/550) showed PD‐L1 expression in TCs, 34.5% (190/550) cases showed PD‐L1 expression in TIICs. There were 45 deficient MMR (dMMR) cases (8.2%), which showed higher rates of PD‐L1 expression compared with MMR‐proficient carcinomas (60.0% vs. 35.2%, P = 0.001). HER2 was positive in 66 (12.0%) cases. The expression of PD‐L1 occurred more frequently in HER2‐negative group than HER2‐positive cohorts (39.0% vs. 24.2%, P = 0.020). The survival analysis revealed that PD‐L1 was not associated with prognosis. This study evaluated the association between the PD‐L1 expression and a specific subgroup (dMMR and HER2‐negative) in a large Asian cohort of GC. GC patients with dMMR and HER2‐negative status exhibited higher PD‐L1 expression rates. Our finding indicated that MMR and HER‐2 status might be potential biomarkers for anti‐PD‐L1 therapy.

Objectives: Programmed death 1 (PD-1) is an immunoinhibitory receptor and has been identified as a new target for immunotherapy in cancer. Here we report the expression of PD-1 ligand 1 (PD-L1) in surgically resected gastric cancer. Materials and Methods: We examined formalin-fixed tumor samples from 144 gastric cancer patients with a primary diagnosis of gastric carcinoma. Immunohistochemistry was used to detect PD-L1. Human epidermal growth factor receptor 2 (HER2) expression and phosphatase and tensin homolog (PTEN) loss of heterozygosity were investigated in these patients. RNA interference was used to downregulate HER2 expression, and PD-L1 protein expression was assessed by flow cytometry using the gastric cancer cell line MKN45. Results: Overexpression of PD-L1 was significantly correlated with tumor invasion (p = 0.011) and associated with poor survival. The number of PD-L1-positive cases increased according to the HER2 score in clinical samples. siRNA-mediated downregulation of HER2 significantly decreased PD-L1 protein expression in MKN45 cells. Conclusions: PD-L1 expression was associated with poor survival of gastric cancer, and HER2 signaling affects the expression of PD-L1 in gastric cancer. In gastric cancer, PTEN and HER2 are potential candidate biomarkers for developing human antibodies that block PD-L1.

Gastric cancer is not a top-10 malignancy in the United States but represents one of the most common causes of cancer death worldwide. Biological differences between tumors from Eastern and Western countries add to the complexity of identifying standard-of-care therapy based on international trials. Systemic chemotherapy, radiotherapy, surgery, immunotherapy, and targeted therapy all have proven efficacy in gastric adenocarcinoma; therefore, multidisciplinary treatment is paramount to treatment selection. Triplet chemotherapy for resectable gastric cancer is now accepted and could represent a plateau of standard cytotoxic chemotherapy for localized disease. Classification of gastric cancer based on molecular subtypes is providing an opportunity for personalized therapy. Biomarkers, in particular microsatellite instability (MSI), programmed cell death ligand 1 (PD-L1), human epidermal growth factor receptor 2 (HER2), tumor mutation burden, and Epstein-Barr virus, are increasingly driving systemic therapy approaches and allowing for the identification of populations most likely to benefit from immunotherapy and targeted therapy. Significant research opportunities remain for the less differentiated histologic subtypes of gastric adenocarcinoma and those without markers of immunotherapy activity.

BackgroundThe prognosis of gastric cancer (GC) patients with human epidermal growth factor receptor 2 (HER2) positive was poor. To illustrate the underlying effective and distinctive molecular characteristics of programmed cell death protein 1 (PD-1) blockade in the treatment of GC with HER2 positive, we analyzed the survival outcome of PD-1 inhibitors combination regimen as the first-line treatment for GC patients with HER2-positive in China.MethodsThis retrospective real-world study compared the prognoses of first-line systemic treatment of PD-1 inhibitors combined with trastuzumab and chemotherapy (PTC group) and trastuzumab and chemotherapy (TC group) in Chinese patients with HER2-positive GC, and then further to identify the specific and molecular characteristics of PD-1 inhibitors treatment by hierarchical analysis. The patients were matched using propensity score matching (PSM). Overall survival (OS) and progression-free survival (PFS) were used as the primary and secondary endpoints of the study.ResultsA total of 95 patients with HER2-positive GC receiving first-line treatment at Zhongshan Hospital of Fudan University from January 2019 to September 2022 were included. The median OS (24.67 vs. 16.00 months, P=0.01) and median PFS (15.57 vs. 7.57 months, P=0.008) of patients with HER2-positive GC who received PTC regimen were longer than those treated by TC regimen as first-line systemic treatment after PSM analysis. In hierarchical analysis, we discovered that programmed cell death ligand 1 (PD-L1) positive expression in tumor tissues was not a predictor of PD-1 inhibitors in HER2-positive GC. However, PD-L1 was an indicator of better survival outcomes by combined trastuzumab treatment in all GC patients. Furthermore, in the subgroup analysis, we found that the median OS for the PTC group was longer by nearly 8 months than the TC group in patients with HER2 gene copy number [HER2 fluorescence in situ hybridization (FISH) test] more than six, while the median OS for the PTC group was longer by approximately 12 months than the TC group in patients with HER2-positive GC with TP53 mutations.ConclusionsThe results suggested that patients with HER2-positive GC could benefit from PD-1 inhibitors combination with trastuzumab and chemotherapy, especially patients with HER-2 FISH more than six and TP53 mutations.

Nivolumab plus chemotherapy in the first-line setting has demonstrated clinical efficacy in patients with human epidermal growth factor receptor 2–negative advanced or metastatic gastric cancer, and is currently indicated as a standard treatment. Programmed death-ligand 1 (PD-L1) expression is an important biomarker for predicting response to anti–programmed death 1/PD-L1 agents in several solid tumors, including gastric cancer. In the CheckMate-649 trial, significant clinical improvements were observed in patients with PD-L1 combined positive score (CPS) ≥ 5, determined using the 28-8 pharmDx assay. Accordingly, an accurate interpretation of PD-L1 CPS, especially at a cutoff of 5, is important. The CPS method evaluates both immune and tumor cells and provides a comprehensive assessment of PD-L1 expression in the tumor microenvironment of gastric cancer. However, CPS evaluation has several limitations, one of which is poor interobserver concordance among pathologists. Despite these limitations, clinical indications relying on PD-L1 CPS are increasing. In response, Korean gastrointestinal pathologists held a consensus meeting for the interpretation of PD-L1 CPS in gastric cancer. Eleven pathologists reviewed 20 PD-L1 slides with a CPS cutoff close to 5, stained with the 28-8 pharmDx assay, and determined the consensus scores. The issues observed in discrepant cases were discussed. In this review, we present cases of gastric cancer with consensus PD-L1 CPS. In addition, we briefly touch upon current practices and clinical issues associated with assays used for the assessment of PD-L1 expression in gastric cancer.