Sporadic Early-Onset Diffuse Gastric Cancers Have High Frequency of Somatic CDH1 Alterations, but Low Frequency of Somatic RHOA Mutations Compared With Late-Onset Cancers

A mathematical simulation model to determine the optimal endoscopic screening strategy for detection of H. pylori-naïve gastric neoplasms

BACKGROUND

The effectiveness of esophagogastroduodenoscopy (EGD) screening in cohorts with low Helicobacter pylori prevalence is unknown. This study aimed to develop an optimally efficient EGD screening strategy for detecting H. pylori-naïve gastric neoplasms (HpNGNs).

METHODS

EGD data of 12 institutions from 2016 to 2022 were retrospectively analyzed. Age-related HpNGN prevalence, tumor growth rate, missing rate, and detection threshold size were calculated from the databases. Subsequently, using clinical data, a novel mathematical model that simultaneously simulated demographic changes and HpNGN detection was developed. Screening strategies using different starting ages (40/45/50 years) and intervals (2/5/10 years) were also compared. The detection rates of all tumors occurring within the virtual cohort and number-needed-to-test (NNT) were measured as outcomes.

RESULTS

Data of 519,368 EGDs and 97 HpNGNs (34 pure signet ring cell carcinomas, 26 gastric adenocarcinomas of the fundic gland type, 30 foveolar gastric adenoma-Raspberry type, and seven undifferentiated-type cancer cases) were analyzed. A virtual cohort with a 70-year time horizon was used to simulate the occurrence, growth, and detection of 346,5836 people. Among the strategies with detection rate > 50%, the screening strategy with a 5-year interval starting at 45 years of age had the lowest NNT. Adopting this strategy, most HpNGNs were detected at < 20 mm in size, and the deep submucosal invasion rate was less than 30%.

CONCLUSIONS

A mathematical simulation model revealed that screening every 5 years starting at 45 years of age could efficiently assist in identifying HpNGNs at an early stage.

The preclinical discovery and development of zolbetuximab for the treatment of gastric cancer

INTRODUCTION

Gastric cancer remains a formidable challenge in oncology with high mortality rates and few advancements in treatment. Claudin-18.2 (CLDN18.2) is a tight junction protein primarily expressed in the stomach and is frequently overexpressed in certain subsets of gastric cancers. Targeting CLDN18.2 with monoclonal antibodies, such as zolbetuximab (IMAB362), has shown promising efficacy results in combination with chemotherapy.

AREAS COVERED

The molecular cell biology of CLDN18.2 is discussed along with studies demonstrating the utility of CLDN18.2 expression as a biomarker and therapeutic target. Important clinical studies are reviewed, including Phase III trials, SPOTLIGHT and GLOW, which demonstrate the efficacy of zolbetuximab in combination with chemotherapy in patients with CLDN18.2-positive advanced gastric cancer.

EXPERT OPINION

CLDN18.2 is involved in gastric differentiation through maintenance of epithelial barrier function and coordination of signaling pathways, and its expression in gastric cancers reflects a 'gastric differentiation' program. Targeting Claudin-18.2 represents the first gastric cancer specific 'targeted' treatment. Further studies are needed to determine its role within current gastric cancer treatment sequencing, including HER2-targeted therapies and immunotherapies. Management strategies will also be needed to better mitigate zolbetuximab-related treatment side effects, including gastrointestinal (GI) toxicities.

Molecular Classifications in Gastric Cancer: A Call for Interdisciplinary Collaboration

Gastric cancer (GC) is a heterogeneous disease, often diagnosed at advanced stages, with a 5-year survival rate of approximately 20%. Despite notable technological advancements in cancer research over the past decades, their impact on GC management and outcomes has been limited. Numerous molecular alterations have been identified in GC, leading to various molecular classifications, such as those developed by The Cancer Genome Atlas (TCGA) and the Asian Cancer Research Group (ACRG). Other authors have proposed alternative perspectives, including immune, proteomic, or epigenetic-based classifications. However, molecular stratification has not yet transitioned into clinical practice for GC, and little attention has been paid to alternative molecular classifications. In this review, we explore diverse molecular classifications in GC from a practical point of view, emphasizing their relationships with clinicopathological factors, prognosis, and therapeutic approaches. We have focused on classifications beyond those of TCGA and the ACRG, which have been less extensively reviewed previously. Additionally, we discuss the challenges that must be overcome to ensure their impact on patient treatment and prognosis. This review aims to serve as a practical framework to understand the molecular landscape of GC, facilitate the development of consensus molecular categories, and guide the design of innovative molecular studies in the field.

Predictive Factors Associated with Survival in Female Gastric Cancer Patients in Southeast Asia

Introduction

Association of Southeast Asian Nations (ASEAN) countries have high Helicobacter pylori infections, and gastric cancer (GC) is a leading fatal cancer in this region, especially in female patients. This study aimed to compare clinical manifestations, histopathological subtypes, and prognostic factors associated with the overall survival rate of female GC patients in this important region.

Methods

This retrospective cohort study was conducted between 2007 and 2022 at a tertiary care center in Thailand. All clinical information, endoscopic findings, and histological types were extensively reviewed. Furthermore, all qualified studies in ASEAN published in PubMed and Scopus between 2000 and 2022 were extracted and thoroughly analyzed. Young female GC patients are defined as those ≤50 years of age.

Results

A total of 98 Thai female GC patients were included, with a mean age of 58.99 ± 14 years; 70.4% were elderly women. The common presenting symptoms were weight loss (69.4%) and dyspepsia (68.4%). Younger female GC patients had significantly more common diffuse-type GC than elderly female GC patients (82.8% vs. 53.6%, p-value = 0.007). Moreover, elderly female GC patients demonstrated significantly better survival than younger female GC patients (44.8% vs. 20.7%, odds ratio = 3.49; 95% confidence interval: 1.20-10.14, p-value = 0.022). Furthermore, a total of 1,491 female GC patients from ASEAN were reviewed and included in this study, aged 15 to 93 years. The top three countries with the highest proportion of female GC from ASEAN were Indonesia (66.7%), Thailand (44.9%), and Singapore (38.4%).

Conclusion

GC in women is not uncommon in ASEAN and presents at an advanced stage with a grave prognosis. This study showed that ASEAN countries with the highest disease burden were Indonesia, Thailand, and Singapore. Overall, survival rates for female GC patients in ASEAN countries were relatively low, highlighting the need for proactive measures such as intensive H. pylori eradication and the development of early detection methods for GC.

A comparison analysis of the somatic mutations in early-onset gastric cancer and traditional gastric cancer

BACKGROUND

Early onset gastric cancer (EOGC) has been on the rise in recent years and differs slightly in pathology from traditional gastric cancer (TGC). Somatic mutations have an essential role in the development of gastric cancer. We aimed to investigate these two types of gastric cancers at the level of somatic mutations and to further understanding of gastric cancer development.

METHODS

Somatic mutation, copy number variation (CNV), and clinical information were obtained from TCGA and UCSC Xena. Samples were divided into EOGC (< 50 years old, N = 28) and TGC (≥ 50 years old, N = 395) groups based on age. R packages "maftools" and "sigminer" were used to identify mutation signatures, while CNV information was processed using GISTIC2.0.

RESULTS

CDH1(21 %, P = 0.030) and ARID1A (28 %, P = 0.014) were more common in EOGC and TGC, respectively. The mutation frequency of ARID1A increased with age, while the opposite was true for CDH1. Sex, Lauren classifications, tumor mutation burden levels, mutation status of TP53, MUC6, NIPBL, KRAS, and copy number variation of the WOOX can affect the activity of the mutant signature.

CONCLUSIONS

Early-onset gastric cancer and traditional gastric cancer have distinct somatic mutation signatures, each with its own relatively specific high-frequency mutated genes, and the gene's mutation frequency correlates with age. Several clinical factors and genetic status affect the activity of some mutational features in gastric cancer in both groups.

Efficacy and safety of chemotherapy in young patients with advanced gastroesophageal adenocarcinoma: data from the Spanish AGAMENON-SEOM registry

BACKGROUND

Gastroesophageal adenocarcinoma in young adults (GCYA) counts for 10-15% of diagnoses. Previous studies have mainly focused on surgical outcomes in patients with resectable tumors; however, systemic therapy for advanced GCYA remains under-evaluated. This study aims to assess the efficacy-related outcomes and safety of first-line chemotherapy (CT) in younger versus older patients with advanced gastroesophageal adenocarcinoma.

METHODS

Patients with advanced gastroesophageal adenocarcinoma from the AGAMENON-SEOM registry treated with first-line polychemotherapy between January 2008 and October 2022 were included. We compared clinicopathological features, therapies received, efficacy-related outcomes, and toxicity between individuals aged < and ≥ 45 years.

RESULTS

Out of 3386 patients, 263 (7.8%) were < 45 years. Young patients exhibited a higher proportion of females affected, lower ECOG-PS ≥ 2, fewer comorbidities, and more aggressive disease-related features, such as higher proportion of diffuse subtype, signet-ring cells, plastic linitis, grade 3, peritoneal metastases and metastatic disease at diagnosis. They received more triple-agent combinations and underwent more surgeries in metastatic setting. No significant differences were observed between groups in overall response rate (53.1% vs. 52.3% in < and ≥ 45 years, respectively, p = 0.579), progression-free survival (6.1 vs. 6.83 months, p = 0.158) and overall survival (11.07 vs. 10.81 months, p = 0.82), even after adjusting for potential confounding factors. Grade 3-4 adverse events were comparable in both groups, although toxicity leading to treatment discontinuation was more frequent in older patients.

CONCLUSIONS

In the AGAMENON-SEOM registry, younger patients with GCYA exhibited more aggressive clinicopathological features, and despite receiving more aggressive treatments, similar efficacy outcomes and toxicity profiles were achieved compared to their older counterparts. In the AGAMENON-SEOM registry, GEAC in < 45 years showed more aggressive clinicopathological features and, although treated with more intense first-line CT regimens, similar efficacy outcomes and toxicity were achieved compared to older patients.

Early Immune Changes Support Signet Ring Cell Dormancy in CDH1-Driven Hereditary Diffuse Gastric Carcinogenesis

Stage IA gastric adenocarcinoma, characterized by foci of intramucosal signet ring cells (SRC), is found in nearly all asymptomatic patients with germline pathogenic CDH1 variants and hereditary diffuse gastric cancer syndrome (HDGC). The molecular steps involved in initiating malignant transformation and promoting SRC dormancy in HDGC are unknown. Here, whole-exome bulk RNA sequencing (RNA-seq) of SRCs and adjacent non-SRC epithelium (NEP) was performed on laser-capture microdissected (LCM) regions of interest found in risk-reducing total gastrectomy specimens from patients with HDGC (Clinicaltrials.gov ID: NCT03030404). In total, 20 patients (6 male, 14 female) with confirmed HDGC were identified. Analysis of differentially expressed genes (DEG) demonstrated upregulation of certain individual EMT and proliferation genes. However, no oncogenic pathways were found to be upregulated in SRCs. Rather, SRC regions had significant enrichment in pathways involved in T-cell signaling. CIBERSORTx predicted significant increases in the presence of regulatory T cells (Treg) specific to SRC regions. IHC confirmed an increase in FOXP3+ cells in SRC foci, as well as elevations in CD4+ T cells and HLA-DR staining. In summary, the tumor immune microenvironment is microscopically inseparable from stage IA gastric SRCs using a granular isolation technique. An elevation in CD4+ T cells within SRC regions correlates with clinically observed SRC dormancy, while Treg upregulation represents a potential immune escape mechanism.

IMPLICATIONS

Characterization of the tumor-immune microenvironment in HDGC underscores the potential for the immune system to shape the transcriptional profile of the earliest tumors, which suggests immune-directed therapy as a potential cancer interception strategy in diffuse-type gastric cancer.

The microbiome and rise of early-onset cancers: knowledge gaps and research opportunities

Accumulating evidence indicates an alarming increase in the incidence of early-onset cancers, which are diagnosed among adults under 50 years of age, in the colorectum, esophagus, extrahepatic bile duct, gallbladder, liver, stomach, pancreas, as well as the bone marrow (multiple myeloma), breast, head and neck, kidney, prostate, thyroid, and uterine corpus (endometrium). While the early-onset cancer studies have encompassed research on the wide variety of organs, this article focuses on research on digestive system cancers. While a minority of early-onset cancers in the digestive system are associated with cancer-predisposing high penetrance germline genetic variants, the majority of those cancers are sporadic and multifactorial. Although potential etiological roles of diets, lifestyle, environment, and the microbiome from early life to adulthood (i.e. in one's life course) have been hypothesized, exact contribution of each of these factors remains uncertain. Diets, lifestyle patterns, and environmental exposures have been shown to alter the oral and intestinal microbiome. To address the rising trend of early-onset cancers, transdisciplinary research approaches including lifecourse epidemiology and molecular pathological epidemiology frameworks, nutritional and environmental sciences, multi-omics technologies, etc. are needed. We review current evidence and discuss emerging research opportunities, which can improve our understanding of their etiologies and help us design better strategies for prevention and treatment to reduce the cancer burden in populations.

Comparison of survival between diffuse type and intestinal type early-onset gastric cancer patients: A large population-based study

Currently, little knowledge about the survival of early-onset gastric cancer and little evidence about the difference of survival based on Lauren type has been reported. In order to investigate the difference, we conducted a retrospective study using the Surveillance, Epidemiology, and End Results (SEER) database and compared it comprehensively. SEER database was used to extracted patients and multiple imputation was utilized to fill blank data. Multivariate cox regression analysis and competing risk model were used to identify the risk factors of survival. K-M survival curve and propensity score matching (PSM) was applied to compare the difference of survival of patients based on Lauren type. Totally, we extracted 3932 EOGC patients including 2086 diffused type and 1846 intestinal type. K-M survival curve showed patients aged 20 to 29 had worse survival compared to patients aged at 30 to 45 years. The survival of EOGC patients would be greatly improved after surgery. Multivariate cox regression analysis revealed diffused type was an independent risk factor, as well as T stage, lymph node metastasis, tumor size (>5 cm) and metastasis, while surgery treatment and examined lymph nodes were protective factors. Multivariate competing risk regression model also showed diffused type was risk factor. We performed PSM by matching 1433 diffused EOGC with 1433 intestinal EOGC patients, finding patients with diffused type had a poorer survival. our results revealed that compared to diffused type EOGC, intestinal type was characterized by a better survival. EOGC should be attached more attention by clinicians.

Biological and clinical implications of early-onset cancers: A unique subtype

In recent years, the incidence of cancers is continuously increasing in young adults. Early-onset cancer (EOC) is usually defined as patients with cancers under the age of 50, and may represent a unique subgroup due to its special disease features. Overall, EOCs often initiate at a young age, present as a better physical performance but high degree of malignancy. EOCs also share common epidemiological and hereditary risk factors. In this review, we discuss several representative EOCs which were well studied previously. By revealing their clinical and molecular similarities and differences, we consider the group of EOCs as a unique subtype compared to ordinary cancers. In consideration of EOC as a rising threat to human health, more researches on molecular mechanisms, and large-scale, prospective clinical trials should be carried out to further translate into improved outcomes.

Combined inhibition of Bcl-2 family members and YAP induces synthetic lethality in metastatic gastric cancer with RASA1 and NF2 deficiency

BACKGROUND

Targetable molecular drivers of gastric cancer (GC) metastasis remain largely unidentified, leading to limited targeted therapy options for advanced GC. We aimed to identify molecular drivers for metastasis and devise corresponding therapeutic strategies.

METHODS

We performed an unbiased in vivo genome-wide CRISPR/Cas9 knockout (KO) screening in peritoneal dissemination using genetically engineered GC mouse models. Candidate genes were validated through in vivo transplantation assays using KO cells. We analyzed target expression patterns in GC clinical samples using immunohistochemistry. The functional contributions of target genes were studied through knockdown, KO, and overexpression approaches in tumorsphere and organoid assays. Small chemical inhibitors against Bcl-2 members and YAP were tested in vitro and in vivo.

RESULTS

We identified Nf2 and Rasa1 as metastasis-suppressing genes through the screening. Clinically, RASA1 mutations along with low NF2 expression define a distinct molecular subtype of metastatic GC exhibiting aggressive traits. NF2 and RASA1 deficiency increased in vivo metastasis and in vitro tumorsphere formation by synergistically amplifying Wnt and YAP signaling in cancer stem cells (CSCs). NF2 deficiency enhanced Bcl-2-mediated Wnt signaling, conferring resistance to YAP inhibition in CSCs. This resistance was counteracted via synthetic lethality achieved by simultaneous inhibition of YAP and Bcl-2. RASA1 deficiency amplified the Wnt pathway via Bcl-xL, contributing to cancer stemness. RASA1 mutation created vulnerability to Bcl-xL inhibition, but the additional NF2 deletion conferred resistance to Bcl-xL inhibition due to YAP activation. The combined inhibition of Bcl-xL and YAP synergistically suppressed cancer stemness and in vivo metastasis in RASA1 and NF2 co-deficiency.

CONCLUSION

Our research unveils the intricate interplay between YAP and Bcl-2 family members, which can lead to synthetic lethality, offering a potential strategy to overcome drug resistance. Importantly, our findings support a personalized medicine approach where combined therapy targeting YAP and Bcl-2, tailored to NF2 and RASA1 status, could effectively manage metastatic GC.

Palliative Gastrectomy Improves the Survival of Patients with Metastatic Early-Onset Gastric Cancer: A Retrospective Cohort Study

Background: Recent studies have found that patients with incurable gastric cancer might benefit from palliative gastrectomy, but the impact of palliative gastrectomy on metastatic early-onset gastric cancer (mEOGC) patients remains unclear. Methods: We analyzed mEOGC patients enrolled in the Surveillance, Epidemiology, and End Results registry from January 2004 to December 2018. Propensity score matching (PSM) analysis with 1:1 matching and the nearest-neighbor matching method were used to ensure well-balanced characteristics between the groups of patients with palliative gastrectomy and those without surgery. Kaplan-Meier survival analysis and Cox proportional hazards regression models were used to evaluate the overall survival (OS) and cause-specific survival (CSS) risk with corresponding 95% confidence intervals (CIs). Results: Of 3641 mEOGC patients, 442 (12.1%) received palliative gastrectomy. After PSM, 596 patients were included in the analysis, with 298 in each group. For the matched cohort, the median survival was 8 months, and the 5-year survival was 4.0%. The median OS of mEOGC patients undergoing palliative gastrectomy was significantly longer than that of patients without surgery (13 months vs. 6 months, p < 0.001), and palliative gastrectomy remained an independent protective factor after adjusting for confounders (HR 0.459, 95% CI 0.382-0.552, p < 0.001), and the protective effect was robust in the subgroup analysis. Similar results were indicated in CSS. Stratified analyses by treatment modality also warranted the superiority of palliative-gastrectomy-based treatment in improving OS and CSS. Conclusions: mEOGC patients with palliative gastrectomy had a significantly longer survival time than patients without surgery. Exploratory analysis confirmed that surgery-based therapy modality was superior in improving survival time.

Evolution of immune and stromal cell states and ecotypes during gastric adenocarcinoma progression

Understanding tumor microenvironment (TME) reprogramming in gastric adenocarcinoma (GAC) progression may uncover novel therapeutic targets. Here, we performed single-cell profiling of precancerous lesions, localized and metastatic GACs, identifying alterations in TME cell states and compositions as GAC progresses. Abundant IgA+ plasma cells exist in the premalignant microenvironment, whereas immunosuppressive myeloid and stromal subsets dominate late-stage GACs. We identified six TME ecotypes (EC1-6). EC1 is exclusive to blood, while EC4, EC5, and EC2 are highly enriched in uninvolved tissues, premalignant lesions, and metastases, respectively. EC3 and EC6, two distinct ecotypes in primary GACs, associate with histopathological and genomic characteristics, and survival outcomes. Extensive stromal remodeling occurs in GAC progression. High SDC2 expression in cancer-associated fibroblasts (CAFs) is linked to aggressive phenotypes and poor survival, and SDC2 overexpression in CAFs contributes to tumor growth. Our study provides a high-resolution GAC TME atlas and underscores potential targets for further investigation.

Analysis of genomic and immune intratumor heterogeneity in linitis plastica via multiregional exome and T-cell receptor sequencing

The molecular landscape and the intratumor heterogeneity (ITH) architecture of gastric linitis plastica (LP) are poorly understood. We performed whole-exome sequencing (WES) and T-cell receptor (TCR) sequencing on 40 tumor regions from four LP patients. The landscape and ITH at the genomic and immunological levels in LP tumors were compared with multiple cancers that have previously been reported. The lymphocyte infiltration was further assessed by immunohistochemistry (IHC) in LP tumors. In total, we identified 6339 non-silent mutations from multi-samples, with a median tumor mutation burden (TMB) of 3.30 mutations per Mb, comparable to gastric adenocarcinoma from the Cancer Genome Atlas (TCGA) cohort (P = 0.53). An extremely high level of genomic ITH was observed, with only 12.42%, 5.37%, 5.35%, and 30.67% of mutations detectable across 10 regions within the same tumors of each patient, respectively. TCR sequencing revealed that TCR clonality was substantially lower in LP than in multi-cancers. IHC using antibodies against CD4, CD8, and PD-L1 demonstrated scant T-cell infiltration in the four LP tumors. Furthermore, profound TCR ITH was observed in all LP tumors, with no T-cell clones shared across tumor regions in any of the patients, while over 94% of T-cell clones were restricted to individual tumor regions. The Morisita overlap index (MOI) ranged from 0.21 to 0.66 among multi-regions within the same tumors, significantly lower than that of lung cancer (P = 0.002). Our results show that LP harbored extremely high genomic and TCR ITH and suppressed T-cell infiltration, suggesting a potential contribution to the frequent recurrence and poor therapeutic response of this adenocarcinoma.

Clinical Characteristics and Oncological Outcomes of Surgically Treated Early-Onset Gastric Adenocarcinoma - a Retrospective Cohort Study

Introduction: The incidence of early-onset gastric adenocarcinoma (patients <50 years, EOGA) is rising. Tumors in younger patients are associated with prognostically unfavorable features. The impact of EOGA on patient survival, however, remains unclear. The aim of this study is to evaluate early-onset age as a prognostic factor compared to late-onset gastric adenocarcinoma (LOGA, >50years) in a surgical cohort and assess treatment options. Methods: We analyzed 738 patients (129 early-onset/609 late-onset) operated in curative intent from 2002 to 2021. Data was extracted from a prospectively managed database of an academic tertiary referral hospital. Differences in perioperative as well as oncological outcomes were calculated by chi-square test. Cox regression analysis was performed to assess disease-free survival (DFS) and overall survival (OS). Results: EOGA patients were more often treated with neoadjuvant therapy (62.8% vs. 43.7%, p<0.001) and extended surgical resections e.g. through additional resections (36.4% vs. 26.8%, p=0.027). EOGA was more often metastasized into regional lymph nodes (pN+ 67.4% vs. 55.3%, p=0.012) and to distant sites (pM+: 23.3% vs. 12.0%, p=0.001) and was more often poorly differentiated (G3/G4: 91.1% vs. 67.2%, p<0.001). There were no significant differences in overall complication rates (31.0% vs. 36.6%, p=0.227). Survival analysis showed shorter DFS (median DFS 25.6 months vs. not reached, p=0.006) but similar OS (median OS: 50.5 months vs. not reached, p=0.920) in EOGA compared to LOGA. Conclusions: This analysis confirmed that EOGA is associated with more aggressive tumor characteristics. Early-Onset was not a prognostic factor in the multivariate analysis. EOGA patients may be more capable to undergo intensive multimodal therapy including perioperative chemotherapy and extended surgery.

Cadherins and catenins in cancer: connecting cancer pathways and tumor microenvironment

Cadherin-catenin complexes are integral components of the adherens junctions crucial for cell-cell adhesion and tissue homeostasis. Dysregulation of these complexes is linked to cancer development via alteration of cell-autonomous oncogenic signaling pathways and extrinsic tumor microenvironment. Advances in multiomics have uncovered key signaling events in multiple cancer types, creating a need for a better understanding of the crosstalk between cadherin-catenin complexes and oncogenic pathways. In this review, we focus on the biological functions of classical cadherins and associated catenins, describe how their dysregulation influences major cancer pathways, and discuss feedback regulation mechanisms between cadherin complexes and cellular signaling. We discuss evidence of cross regulation in the following contexts: Hippo-Yap/Taz and receptor tyrosine kinase signaling, key pathways involved in cell proliferation and growth; Wnt, Notch, and hedgehog signaling, key developmental pathways involved in human cancer; as well as TGFβ and the epithelial-to-mesenchymal transition program, an important process for cancer cell plasticity. Moreover, we briefly explore the role of cadherins and catenins in mechanotransduction and the immune tumor microenvironment.

Early-Onset Cancer in the Gastrointestinal Tract Is on the Rise-Evidence and Implications

Epidemiologic data indicate a significant increase in the incidence of colorectal cancer in younger populations in the past three decades. Moreover, recent evidence also demonstrates a similar trend in gastric, pancreatic, and biliary tract cancers. A majority of these early-onset cases are sporadic and lack hereditary or familial background, implying a potential key role for behavioral, lifestyle, nutritional, microbial, and environmental factors. This review explores the current data on early-onset gastrointestinal cancer, exploring the etiology, unique treatment considerations for this population, future challenges, as well as implications for research and practice.

SIGNIFICANCE

The worrisome trend of an increasing incidence of early-onset gastrointestinal cancers appears to be correlated with nonhereditary etiologies in which behavioral, lifestyle, nutritional, microbial, and environmental factors, as well as host mechanisms, may play a key role. Further epidemiologic and pathogenetic research is urgently needed to better understand the underlying mechanisms and to develop preventive strategies and tailored early detection. Young patients with gastrointestinal cancer face unique challenges and unmet needs. These must be addressed in the future management of the disease to minimize treatment-related somatic morbidity and prevent psychosocial sequelae.

Non-hereditary early onset gastric cancer: An unmet medical need

Gastric cancer (GC) is a lethal disease and the diagnosis in the young population is a major challenge from both individual and social point of views. Early-onset GC accounts for ∼5% of GC; among them, 3% are part of a hereditary syndrome and the majority are sporadic. However, even if the early-onset forms were less frequent in the past, the increasing number in the last decades has improved the interest and awareness of them in the society and in the scientific community. In particular, the different behaviour and characteristics of early-onset GC suggest that it is a completely different entity, which requires a tailored and personalized management. Here we provide an updated overview about non-hereditary early-onset GC, which is an unmet clinical need today, along with future perspectives in this field.

Comprehensive transcriptomic profiling and mutational landscape of primary gastric linitis plastica

BACKGROUND

Primary gastric linitis plastica (GLP) is a distinct phenotype of gastric cancer with poor survival. Comprehensive molecular profiles and putative therapeutic targets of GLP remain undetermined.

METHODS

We subjected 10 tumor-normal tissue pairs to whole exome sequencing (WES) and whole transcriptome sequencing (WTS). 10 tumor samples were all GLP which involves 100% of the gastric wall macroscopically. TCGA data were compared to generate the top mutated genes and the overexpressed genes in GLP.

RESULTS

Our results reveal that GLP has distinctive genomic and transcriptomic features, dysfunction in the Hippo pathway is likely to be a key step during GLP development. 6 genes were identified as significantly highly mutated genes in GLP, including AOX1, ANKRD36C, CPXM1, PTPN14, RPAP1, and DCDC1). MUC6, as a previously identified gastric cancer driver gene, has a high mutation rate (20%) in GLP. 20% of patients in our GLP cohort had CDH1 mutations, while none had RHOA mutations. GLP exhibits high immunodeficiency and low AMPK pathway activity. Our WTS results showed that 3 PI3K-AKT pathway-related genes (PIK3R2, AKT3, and IGF1) were significantly up-regulated in GLP. Two genes were identified using immunohistochemistry (IHC), IGF2BP3 and MUC16, which specifically expressed in diffuse-type-related gastric cancer cell lines, and its knockdown inhibits PI3K-AKT pathway activity.

CONCLUSIONS

We provide the first integrative genomic and transcriptomic profiles of GLP, which may facilitate its diagnosis, prognosis, and treatment.

Molecular pathogenesis, targeted therapies, and future perspectives for gastric cancer

Gastric cancer is a major source of global cancer mortality with limited treatment options and poor patient survival. As our molecular understanding of gastric cancer improves, we are now beginning to recognize that these cancers are a heterogeneous group of diseases with incredibly unique pathogeneses and active oncogenic pathways. It is this molecular diversity and oftentimes lack of common oncogenic driver mutations that bestow the poor treatment responses that oncologists often face when treating gastric cancer. In this review, we will examine the treatments for gastric cancer including up-to-date molecularly targeted therapies and immunotherapies. We will then review the molecular subtypes of gastric cancer to highlight the diversity seen in this disease. We will then shift our discussion to basic science and gastric cancer mouse models as tools to study gastric cancer molecular heterogeneity. Furthermore, we will elaborate on a molecular process termed paligenosis and the cyclical hit model as key events during gastric cancer initiation that impart nondividing mature differentiated cells the ability to re-enter the cell cycle and accumulate disparate genomic mutations during years of chronic inflammation and injury. As our basic science understanding of gastric cancer advances, so too must our translational and clinical efforts. We will end with a discussion regarding single-cell molecular analyses and cancer organoid technologies as future translational avenues to advance our understanding of gastric cancer heterogeneity and to design precision-based gastric cancer treatments. Elucidation of interpatient and intratumor heterogeneity is the only way to advance future cancer prevention, diagnoses and treatment.

Genomic features of Helicobacter pylori-naïve diffuse-type gastric cancer

Helicobacter pylori (HP) is a major etiologic driver of diffuse-type gastric cancer (DGC). However, improvements in hygiene have led to an increase in the prevalence of HP-naïve DGC; that is, DGC that occurs independent of HP. Although multiple genomic cohort studies for gastric cancer have been conducted, including studies for DGC, distinctive genomic differences between HP-exposed and HP-naïve DGC remain largely unknown. Here, we employed exome and RNA sequencing with immunohistochemical analyses to perform binary comparisons between 36 HP-exposed and 27 HP-naïve DGCs from sporadic, early-stage, and intramucosal or submucosal tumor samples. Among the samples, 33 HP-exposed and 17 HP-naïve samples had been preserved as fresh-frozen samples. HP infection status was determined using stringent criteria. HP-exposed DGCs exhibited an increased single nucleotide variant burden (HP-exposed DGCs; 1.97 [0.48-7.19] and HP-naïve DGCs; 1.09 [0.38-3.68] per megabase; p = 0.0003) and a higher prevalence of chromosome arm-level aneuploidies (p < 0.0001). CDH1 was mutated at similar frequencies in both groups, whereas the RHOA-ARHGAP pathway misregulation was exclusive to HP-exposed DGCs (p = 0.0167). HP-exposed DGCs showed gains in chromosome arms 8p/8q (p < 0.0001), 7p (p = 0.0035), and 7q (p = 0.0354), and losses in 16q (p = 0.0167). Immunohistochemical analyses revealed a higher expression of intestinal markers such as CD10 (p < 0.0001) and CDX2 (p = 0.0002) and a lower expression of the gastric marker, MUC5AC (p = 0.0305) among HP-exposed DGCs. HP-naïve DGCs, on the other hand, had a purely gastric marker phenotype. This work reveals that HP-naïve and HP-exposed DGCs develop along different molecular pathways, which provide a basis for early detection strategies in high incidence settings. © 2022 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Is early-onset cancer an emerging global epidemic? Current evidence and future implications

Over the past several decades, the incidence of early-onset cancers, often defined as cancers diagnosed in adults <50 years of age, in the breast, colorectum, endometrium, oesophagus, extrahepatic bile duct, gallbladder, head and neck, kidney, liver, bone marrow, pancreas, prostate, stomach and thyroid has increased in multiple countries. Increased use of screening programmes has contributed to this phenomenon to a certain extent, although a genuine increase in the incidence of early-onset forms of several cancer types also seems to have emerged. Evidence suggests an aetiological role of risk factor exposures in early life and young adulthood. Since the mid-20th century, substantial multigenerational changes in the exposome have occurred (including changes in diet, lifestyle, obesity, environment and the microbiome, all of which might interact with genomic and/or genetic susceptibilities). However, the effects of individual exposures remain largely unknown. To study early-life exposures and their implications for multiple cancer types will require prospective cohort studies with dedicated biobanking and data collection technologies. Raising awareness among both the public and health-care professionals will also be critical. In this Review, we describe changes in the incidence of early-onset cancers globally and suggest measures that are likely to reduce the burden of cancers and other chronic non-communicable diseases.

Ethnic Disparities in Early-Onset Gastric Cancer: A Population-Based Study in Texas and California

BACKGROUND

Incidence rates of gastric cancer are increasing in young adults (age &lt;50 years), particularly among Hispanic persons. We estimated incidence rates of early-onset gastric cancer (EOGC) among Hispanic and non-Hispanic White persons by census tract poverty level and county-level metro/nonmetro residence.

METHODS

We used population-based data from the California and Texas Cancer Registries from 1995 to 2016 to estimate age-adjusted incidence rates of EOGC among Hispanic and non-Hispanic White persons by year, sex, tumor stage, census tract poverty level, metro versus nonmetro county, and state. We used logistic regression models to identify factors associated with distant stage diagnosis.

RESULTS

Of 3,047 persons diagnosed with EOGC, 73.2% were Hispanic White. Incidence rates were 1.29 [95% confidence interval (CI), 1.24-1.35] and 0.31 (95% CI, 0.29-0.33) per 100,000 Hispanic White and non-Hispanic White persons, respectively, with consistently higher incidence rates among Hispanic persons at all levels of poverty. There were no statistically significant associations between ethnicity and distant stage diagnosis in adjusted analysis.

CONCLUSIONS

There are ethnic disparities in EOGC incidence rates that persist across poverty levels.

IMPACT

EOGC incidence rates vary by ethnicity and poverty; these factors should be considered when assessing disease risk and targeting prevention efforts.

Variation in Treatment Patterns of Patients with Early-Onset Gastric Cancer

Background: Early-onset gastric cancer (EOGC), or gastric cancer in patients younger than 45 years old, is poorly understood and relatively uncommon. Similar to other gastrointestinal malignancies, the incidence of EOGC is rising in Western countries. It is unclear which populations experience a disproportionate burden of EOGC and what factors influence how patients with EOGC are treated. Methods: We conducted a retrospective, population-based study of patients diagnosed with gastric cancer from 2004 to 2018 using the National Cancer Database (NCDB). In addition to identifying unique demographic characteristics of patients with EOGC, we evaluated (using multivariable logistic regression controlling for year of diagnoses, primary site, and stage) how gender/sex, race/ethnicity, treatment facility type, payor status, and location of residence influenced the receipt of surgery, chemotherapy, and radiation. Results: Compared to patients 45−70 and >70 years of age with gastric cancer, patients with EOGC were more likely to be female, Asian/Pacific Islander (PI), African American (AA), Hispanic, uninsured, and present with stage IV disease. On multivariable analysis, several differences among subsets of patients with EOGC were identified. Female patients with EOGC were less likely to receive surgery and chemotherapy than male patients with EOGC. Asian/Pacific Islander patients with EOGC were more likely to receive chemotherapy and less likely to receive radiation than Caucasian patients with EOGC. African American patients were more likely to receive chemotherapy than Caucasian patients with EOGC. Hispanic patients were more likely to receive surgery and chemotherapy and less likely to receive radiation than Caucasian patients with EOGC. Patients with EOGC treated at community cancer centers were more likely to receive surgery and less likely to receive chemotherapy than patients with EOGC treated at academic centers. Uninsured patients with EOGC were more likely to receive surgery and less likely to receive chemotherapy than privately insured patients with EOGC. Patients with EOGC living in locations not adjacent to metropolitan areas were less likely to receive surgery compared to patients with EOGC who resided in metropolitan areas, Conclusions: Patients with EOGC are a demographically distinct population. Treatment of these patients varies significantly based on several demographic factors. Additional analysis is needed to elucidate why particular groups are more affected by EOGC and how treatment decisions are made for, and by, these patients.

The immune microenvironment in gastric adenocarcinoma

Like most solid tumours, the microenvironment of epithelial-derived gastric adenocarcinoma (GAC) consists of a variety of stromal cell types, including fibroblasts, and neuronal, endothelial and immune cells. In this article, we review the role of the immune microenvironment in the progression of chronic inflammation to GAC, primarily the immune microenvironment driven by the gram-negative bacterial species Helicobacter pylori. The infection-driven nature of most GACs has renewed awareness of the immune microenvironment and its effect on tumour development and progression. About 75-90% of GACs are associated with prior H. pylori infection and 5-10% with Epstein-Barr virus infection. Although 50% of the world's population is infected with H. pylori, only 1-3% will progress to GAC, with progression the result of a combination of the H. pylori strain, host susceptibility and composition of the chronic inflammatory response. Other environmental risk factors include exposure to a high-salt diet and nitrates. Genetically, chromosome instability occurs in ~50% of GACs and 21% of GACs are microsatellite instability-high tumours. Here, we review the timeline and pathogenesis of the events triggered by H. pylori that can create an immunosuppressive microenvironment by modulating the host's innate and adaptive immune responses, and subsequently favour GAC development.

Somatic Alteration Characteristics of Early-Onset Gastric Cancer

Gastric cancer is one of the most common and deadly cancer types worldwide, which brings millions of dollars of economic loss each year. Patients diagnosed with early-onset gastric cancer were reported to have a worse prognosis compared to other gastric cancer patients, while the mechanisms behind such phenomenon are unknown. To identify age-dependent somatic alternations in gastric cancer, next-generation sequencing targeting 425 genes was performed on 1688 gastric tumor tissues and corresponding plasma samples. In our study, the microsatellite instability (MSI) and chromosomal instability score (CIS) values increased along with the age of patients, which indicates that older patients display a less genomic stability pattern. The differences of somatic alternations between young and old groups were compared. Somatic mutations CDH1 and copy number gains of FGFR2 were identified to enrich in the younger gastric cancer patients, which may contribute to the worse prognosis of early-onset gastric cancer patients.

Clinicopathological characteristics, survival outcome and prognostic factors of very young gastric cancer

To explore the clinicopathological characteristics, survival outcomes, and prognosis of very young gastric cancer (GC). From January 1, 2011 to January 1, 2021, GC patients under 30 years old treated in three tertiary hospitals were enrolled. Clinicopathological characteristics were summarized, prognostic factors and survival outcomes including overall survival (OS), disease-free survival (DFS), and progression-free survival (PFS) were retrospectively analyzed. One hundred patients were finally included, with a median age of 23 years.73 (73.0%) were female. Most patients had initial symptoms of abdominal pain (66.0%). The most common tumor locations were gastric antrum (38.0%) and gastric body (37.0%). The main histological types were diffuse (81.0%) and poorly differentiated (91.0%). Most patients presented with stage III-IV disease (82.0%) at diagnosis and the common sites of metastasis were ovary (39.5%) and peritoneum (27.6%). The mOS of the whole group was 23.3 months (95% CI 17.2-29.4). Moreover, the mOS of patients at stage I-II was not reached. The mOS of patients at stage III and stage IV was 40.6 months (95% CI 10.2-70.9) and 10.3 months (95% CI 8.9-11.6), respectively. The mDFS of stage I-III patients was 28.5 months (95% CI 14.7-42.3), and the mPFS of the metastatic patients was 4.5 months (95% CI 4.0-5.0). TNM stage (P = 0.005) and radical surgery (P = 0.001) were independent prognostic factors of overall survival. The very young GC were predominantly female, diffuse type, and advanced diagnosis. TNM stage and radical surgery were independent prognosis factors for overall survival.

Poorly Cohesive Carcinoma of the Nonampullary Small Intestine: A Distinct Histologic Subtype With Prognostic Significance

Poorly cohesive carcinomas (PCCs) are neoplasms characterized by a dyshesive cell invasion pattern featuring single-cell or cord-like stromal infiltration. Although they have been extensively studied in the stomach and other digestive system organs, limited data regarding nonampullary small bowel poorly cohesive carcinomas (SB-PCCs) are hitherto available. The aims of our study were to analyze the clinicopathologic and immunophenotypical features of SB-PCCs (PCC pattern accounting for >50% of the neoplasm) and to compare them with small bowel adenocarcinomas (SBAs), not otherwise specified (SBAs-NOS) and with cancers with a histologically distinct PCC component accounting for 10% to 50% of the neoplasm (mixed-poorly-cohesive-glandular-SBAs). Fifteen SB-PCCs were identified and compared with 95 SBAs-NOS and 27 mixed-poorly-cohesive-glandular-SBAs. Most SB-PCCs (67%) were composed of <10% of signet-ring cells, and all but 1 SB-PCCs exhibited loss of membranous expression of E-cadherin. Compared with SBAs-NOS, SB-PCCs showed a significantly younger patient age at diagnosis, and a stronger association with Crohn disease, and both SB-PCCs and mixed-poorly-cohesive-glandular-SBAs featured a higher rate of lymphovascular and perineural invasion and a lower percentage of mismatch repair-deficient cases. Importantly, the cancer-specific survival of SB-PCC (hazard ratio: 3.81; 95% confidence interval: 1.90-7.64; P<0.001) and mixed-poorly-cohesive-glandular-SBA (4.12; 2.20-7.71; P<0.001) patients was significantly worse compared with SBAs-NOS cases. This study provides objective evidence to the World Health Organization (WHO) 2019 introduction of SB-PCC as a distinctive subtype of nonampullary SBA, by virtue of its unique clinical and histologic features, and suggests that both SB-PCCs and mixed-poorly-cohesive-glandular-SBAs should be separated from SBAs-NOS.

Diffuse-type Gastric Cancer

Gastric cancer is the most prevalent malignant tumor in Korea. Histologically, it is often classified into intestinal-type and diffuse-type. Intestinal-type gastric cancer is known to occur mainly from chronic gastritis caused by Helicobacter pylori (H. pylori) through atrophic gastritis and intestinal metaplasia, a precancerous change of the mucosa, whereas diffuse-type gastric cancer is caused by H. pylori infection, wherein active inflammation of the gastric mucosa occurs without precancerous changes in the mucosa. Compared with intestinal-type gastric cancer, it occurs at a young age, there is no difference in male to female ratio, or tends to occur more in women, and is more aggressive than intestinal-type gastric cancer. Intestinal-type gastric cancer is predominant in East Asian populations such as Koreans and Japanese, whereas diffuse-type gastric cancer has more uniform geographic distribution. In the present manuscript, I have reviewed diffuse-type gastric cancer, distinct from intestinal-type gastric cancer.

The dawn of precision medicine in diffuse-type gastric cancer

Gastric cancer (GC) is one of the most common malignancies worldwide. The histology- and morphology-based Lauren classification of GC has been widely used for over 50 years in clinical practice. The Lauren classification divides GC into intestinal and diffuse types, which have distinct etiology, molecular profiles, and clinicopathological features. Diffuse-type GC (DGC) accounts for approximately 30% of GCs. Tumor cells lack adhesion and infiltrate the stroma as single cells or small subgroups, leading to easy dissemination in the abdominal cavity. Clinically, DGC has aggressive traits with a high risk of recurrence and metastasis, which results in unfavorable prognosis. Although systemic chemotherapy is the main therapeutic approach for recurrent or metastatic GC patients, clinical benefits are limited for patients with DGC. Therefore, it is urgent to develop effective therapeutic strategies for DGC patients. Considerable research studies have characterized the molecular and genomic landscape of DGC, of which tight junction protein claudin-18 isoform 2 (CLDN18.2) and fibroblast growing factors receptor-2 isoform IIIb (FGFR2-IIIb) are the most attractive targets because of their close association with DGC. Recently, the impressive results of two phase II FAST and FIGHT trials demonstrate proof-of-concept, suggesting that anti-CLDN18.2 antibody (zolbetuximab) and FGFR2-IIIb antibody (bemarituzumab) are promising approaches for patients with CLDN18.2-positive and FGFR2-IIIb-positive GC, respectively. In this review, we summarize the clinicopathological features and molecular profiles of DGC and highlight a potential therapeutic target based on the findings of pivotal clinical trials.

The New Era of Immunotherapy in Gastric Cancer

Simple Summary

Advanced gastric cancer remains a malignancy with a poor prognosis, with a median survival of about 12–15 months. In recent years, immune checkpoint inhibitors have emerged as a new standard of care for several malignancies, including advanced gastric cancer, and have demonstrated good clinical benefit in some populations. In this review paper, we describe the current status of immunotherapy in gastric cancer, with a focus on molecular and immunological profiles, biomarkers, major clinical trials, and novel immunotherapies.

Abstract

Immune checkpoint inhibitors (ICIs) such as anti-programmed cell death-1 (PD-1) or programmed cell death ligand-1 (PD-L1) monoclonal antibodies have prolonged survival in various types of malignancies, including advanced gastric cancer (AGC). Nivolumab, a monoclonal anti-PD-1 antibody, showed an improvement in overall survival at a later-line therapy in unselected AGC patients in the ATTRACTION-2 study or in combination with chemotherapy as first-line therapy in the global CheckMate-649 study. Another monoclonal anti-PD-1 antibody, pembrolizumab, showed single agent activity in tumors with high microsatellite instability or high tumor mutational burden. Furthermore, a recent KEYNOTE-811 study demonstrated significant improvement in response rate with pembrolizumab combined with trastuzumab and chemotherapy for HER2-positive AGC. Based on these results, ICIs are now incorporated into standard treatment for AGC patients. As a result of pivotal clinical trials, three anti-PD-1 antibodies were approved for AGC: nivolumab combined with chemotherapy as first-line treatment or nivolumab monotherapy as third- or later-line treatment in Asian countries; pembrolizumab for previously treated microsatellite instability-high (MSI-H) or tumor mutational burden-high AGC, or pembrolizumab combined with trastuzumab and chemotherapy for HER2-positive AGC in the United States; and dostarlimab for previously treated MSI-H AGC in the United States. However, a substantial number of patients have showed resistance to ICIs, highlighting the importance of the better selection of patients or further combined immunotherapy. This review focused on molecular and immunological profiles, pivotal clinical trials of ICIs with related biomarkers, and investigational immunotherapy for AGC.

Multi-omic profiling of peritoneal metastases in gastric cancer identifies molecular subtypes and therapeutic vulnerabilities

Peritoneal metastasis, a hallmark of incurable advanced gastric cancer (GC), presently has no curative therapy and its molecular features have not been examined extensively. Here we present a comprehensive multi-omic analysis of malignant ascitic fluid samples and their corresponding tumor cell lines from 98 patients, including whole-genome sequencing, RNA sequencing, DNA methylation and enhancer landscape. We identify a higher frequency of receptor tyrosine kinase and mitogen-activated protein kinase pathway alterations compared to primary GC; moreover, approximately half of the gene alterations are potentially treatable with targeted therapy. Our analyses also stratify ascites-disseminated GC into two distinct molecular subtypes: one displaying active super enhancers (SEs) at the ELF3, KLF5 and EHF loci, and a second subtype bearing transforming growth factor-β (TGF-β) pathway activation through SMAD3 SE activation and high expression of transcriptional enhancer factor TEF-1 (TEAD1). In the TGF-β subtype, inhibition of the TEAD pathway circumvents therapy resistance, suggesting a potential molecular-guided therapeutic strategy for this subtype of intractable GC.

Higher Lymph Node Metastasis Rate and Poorer Prognosis of Intestinal-Type Gastric Cancer Compared to Diffuse-Type Gastric Cancer in Early-Onset Early-Stage Gastric Cancer: A Retrospective Study

Background: The incidence of early-onset gastric cancer (GC) that was diagnosed at <50 years is increasing, but there is a knowledge gap on early-onset early-stage GC (EEGC) that was defined as early-onset GC limited to the mucosa or submucosa. Therefore, we comprehensively analysed the clinical features based on Lauren type.

Methods: Logistic and Cox analyses were used to investigate risk factors for lymph node metastasis (LNM) and prognosis, respectively. Propensity score matching (PSM) was used to adjust confounding factors. Protein mass spectrometry analysis was used to explore the molecular mechanism of LNM.

Result: Our study included 581 patients with EEGC from the Surveillance, Epidemiology, and End Results (SEER) database and 226 patients with EEGC from our own centre. We identified intestinal type, T1b stage, and tumour size (>3 cm) as risk factors for LNM using SEER and our own data. We also found that the prognosis of patients with intestinal-type EEGC was poorer than patients with diffuse-type EEGC, and T1b stage and positive LNM were hazard factors for survival. After analysing the expression of proteins between positive and negative LNM in the intestinal or diffuse type, we found no similar proteins between these groups. The differentially expressed genes (DEGs) in the intestinal type functioned as epithelial cell signalling in Helicobacter pylori. The DEGs in the diffuse type functioned in the tricarboxylic acid cycle (TCA cycle) and oxidative phosphorylation.

Conclusion: For EEGC, our study was the first report to demonstrate that the intestinal type was a risk factor for LNM and survival compared to the diffuse type, and the oncogenic expression promoting the occurrence of LNM was different. These findings suggest that clinicians should pay more attention to intestinal-type EEGC than diffuse-type EEGC.

The keratin 17/YAP/IL6 axis contributes to E-cadherin loss and aggressiveness of diffuse gastric cancer

DGC is a particular aggressive malignancy with poor prognosis. Recent omics studies characterized DGC with CDH1/E-cadherin loss and EMT-signatures. However, the underlying mechanisms for maintaining the aggressive behavior and molecular features of DGC remain unclear. Here, we find that intermediate filaments KRT17 is significantly lower in DGC tissues than that in intestinal gastric cancer tissues and associated with poor prognosis of DGC. We demonstrate that downregulation of KRT17 induces E-cadherin loss, EMT changes, and metastasis behaviors of GC cells. Mechanistically, the loss of intermediate filaments KRT17 induces reorganization of cytoskeleton, further activates YAP signaling, and increases IL6 expression, which contributes to the enhanced metastasis ability of GC cells. Together, these results indicate that KRT17/YAP/IL6 axis contributes to maintaining E-cadherin loss, EMT feature, and metastasis of DGC, providing a new insight into the role of aberrant intermediate filaments in DGC malignancy.

Histological and mutational profile of diffuse gastric cancer: current knowledge and future challenges

Gastric cancer (GC) pathogenesis is complex and heterogeneous, reflecting morphological, molecular and genetic diversity. Diffuse gastric cancer (DGC) and intestinal gastric cancer (IGC) are the major histological types. GC may be sporadic or hereditary; sporadic GC is related to environmental and genetic low-risk factors and hereditary GC is caused by inherited high-risk mutations, so far identified only for the diffuse histotype. DGC phenotypic heterogeneity challenges the current understanding of molecular mechanisms underlying carcinogenesis. The definition of a DGC-specific mutational profile remains controversial, possibly reflecting the heterogeneity of DGC-related histological subtypes [signet-ring cell carcinoma (SRCC) and poorly cohesive carcinoma not otherwise specified (PCC-NOS)]. Indeed, DGC and DGC-related subtypes may present specific mutational profiles underlying the particularly aggressive behaviour and dismal prognosis of DGC vs IGC and PCC-NOS vs SRCC. In this systematic review, we revised the histological presentations, molecular classifications and approved therapies for gastric cancer, with a focus on DGC. We then analysed results from the most relevant studies, reporting mutational analysis data specifying mutational frequencies, and their relationship with DGC and IGC histological types, and with specific DGC subtypes (SRCC and PCC-NOS). We aimed at identifying histology-associated mutational profiles with an emphasis in DGC and its subtypes (DGC vs IGC; sporadic vs hereditary DGC; and SRCC vs PCC-NOS). We further used these mutational profiles to identify the most commonly affected molecular pathways and biological functions, and explored the clinical trials directed specifically to patients with DGC. This systematic analysis is expected to expose a DGC-specific molecular profile and shed light into potential targets for therapeutic intervention, which are currently missing.

Aberrant expression of SFRP1, SFRP3, DVL2 and DVL3 Wnt signaling pathway components in diffuse gastric carcinoma

Diffuse gastric carcinoma (DGC) is characterized by poorly cohesive cells, highly invasive growth patterns, poor prognosis and resistance to the majority of available systemic therapeutic strategies. It has been previously reported that the Wnt/β-catenin signaling pathway serves a prominent role in the tumorigenesis of gastric carcinoma. However, the mechanism underlying the dysregulation of this pathway in DGC has not been fully elucidated. Therefore, the present study aimed to investigate the expression profiles of Wnt antagonists, secreted frizzled-related protein 1 (SFRP1) and secreted frizzled-related protein 3 (SFRP3), and dishevelled protein family members, dishevelled segment polarity protein 2 (DVL2) and dishevelled segment polarity protein 3 (DVL3), in DGC tissues. The association between the expression levels of these factors and the clinicopathological parameters of the patients was determined. Protein and mRNA expression levels in 62 DGC tumor tissues and 62 normal gastric mucosal tissues obtained from patients with non-malignant disease were measured using immunohistochemical and reverse transcription-quantitative PCR (RT-qPCR) analysis. Significantly lower protein expression levels of SFRP1 (P<0.001) and SFRP3 (P<0.001), but significantly higher protein expression levels of DVL2 (P<0.001) and DVL3 (P<0.001) were observed in DGC tissues compared with in control tissues by immunohistochemistry. In addition, significantly lower expression levels of SFRP1 (P<0.05) and higher expression levels of DVL3 (P<0.05) were found in in DGC tissues compared with those in normal gastric mucosal tissues using RT-qPCR. According to correlation analysis between the SFRP1, SFRP3, DVL2 and DVL3 protein expression levels and the clinicopathological characteristics of patients with DGC, a statistically significant correlation was found between the SFRP3 volume density and T stage (r=0.304; P=0.017) and between the SFRP3 volume density and clinical stage (r=0.336; P=0.008). In conclusion, the findings of the present study suggested that the Wnt signaling pathway components SFRP1, SFRP3, DVL2 and DVL3 may be aberrantly expressed in DGC tissues, implicating their possible role in the development of this malignant disease. The present data also revealed a positive relationship between SFRP3 protein expression and the clinical and T stage of DGC.

A Distinct Clinicopathological Feature and Prognosis of Young Gastric Cancer Patients Aged ≤ 45 Years Old

Purpose

The aim of this retrospective study was to probe into clinicopathological features and prognosis of early-onset gastric cancer (EOGC) patients aged ≤ 45 years old.

Methods

This study selected 154 young gastric cancer patients aged ≤ 45 years old and 158 elderly gastric cancer patients aged > 50 years old admitted to West China Hospital of Sichuan University in 2009-2019 as the research object. These patients were further divided into two groups according to whether tumor can be resected radically. The following parameters were analyzed: age, gender, helicobacter pylori (HP) infection status, Her-2 status, pathological type and stage, chemotherapy, tumor differentiation degree, overall survival (OS).

Results

More than 3,000 patients with gastric carcinoma were screened, and 154 young gastric cancer patients aged ≤ 45 years old were identified as EOGC. Among them, the number of female patients in EOGC group was significantly higher than that of males, accounting for 63.6%. In addition, EOGC were associated with diffuse Laur´en type and poorly differentiated tumors. Interestingly, the Kaplan-Meier method showed that the OS of unresectable EOGC group was significantly lower than that of unresectable LOGC group (P = 0.0005) and chemotherapy containing paclitaxel tended to be more effective in the young people (P = 0.0511). Nevertheless, there was no significant difference in OS between young and elderly patients with gastric cancer in the radical resection group (P = 0.3881).

Conclusion

EOGC patients have a worse prognosis than late-onset gastric cancer (LOGC) patients with advanced unresectable gastric cancer. Palliative surgery or chemotherapy containing paclitaxel may improve the OS of unresectable young individuals with gastric cancer. Additional randomized controlled trials are required for guiding clinical practice.

Indolent feature of Helicobacter pylori-uninfected intramucosal signet ring cell carcinomas with CDH1 mutations

BACKGROUND

In Helicobacter pylori (Hp)-uninfected individuals, diffuse-type gastric cancer (DGC) was reported as the most common type of cancer. However, the carcinogenic mechanism of Hp-uninfected sporadic DGC is largely unknown.

METHODS

We performed whole-exome sequencing of Hp-uninfected DGCs and Hp-uninfected normal gastric mucosa. For advanced DGCs, external datasets were also analyzed.

RESULTS

Eighteen patients (aged 29-78 years) with DGCs and nine normal subjects (28-77 years) were examined. The mutation burden in intramucosal DGCs (10-66 mutations per exome) from individuals aged 29-73 years was not very different from that in the normal gastric glands, which showed a constant mutation accumulation rate (0.33 mutations/exome/year). Unbiased dN/dS analysis showed that CDH1 somatic mutation was a driver mutation for intramucosal DGC. CDH1 mutation was more frequent in intramucosal DGCs (67%) than in advanced DGCs (27%). In contrast, TP53 mutation was more frequent in advanced DGCs (52%) than in intramucosal DGCs (0%). This discrepancy in mutations suggests that CDH1-mutated intramucosal DGCs make a relatively small contribution to advanced DGC formation. Among the 16 intramucosal DGCs (median size, 6.5 mm), 15 DGCs were pure signet ring cell carcinoma (SRCC) with reduced E-cadherin expression and a low proliferative capacity (median Ki-67 index, 2.4%). Five SRCCs reviewed endoscopically over 2-5 years showed no progression.

CONCLUSIONS

Impaired E-cadherin function due to CDH1 mutation was considered as an early carcinogenic event of Hp-uninfected intramucosal SRCC. Genetic and clinical analyses suggest that Hp-uninfected intramucosal SRCCs may be less likely to develop into advanced DGCs.

Biomarker-targeted therapies for advanced-stage gastric and gastro-oesophageal junction cancers: an emerging paradigm

Advances in cancer biology and sequencing technology have enabled the selection of targeted and more effective treatments for individual patients with various types of solid tumour. However, only three molecular biomarkers have thus far been demonstrated to predict a response to targeted therapies in patients with gastric and/or gastro-oesophageal junction (G/GEJ) cancers: HER2 positivity for trastuzumab and trastuzumab deruxtecan, and microsatellite instability (MSI) status and PD-L1 expression for pembrolizumab. Despite this lack of clinically relevant biomarkers, distinct molecular subtypes of G/GEJ cancers have been identified and have informed the development of novel agents, including receptor tyrosine kinase inhibitors and monoclonal antibodies, several of which are currently being tested in ongoing trials. Many of these trials include biomarker stratification, and some include analysis of circulating tumour DNA (ctDNA), which both enables the noninvasive assessment of biomarker expression and provides an indication of the contributions of intratumoural heterogeneity to response and resistance. The results of these studies might help to optimize the selection of patients to receive targeted therapies, thus facilitating precision medicine approaches for patients with G/GEJ cancers. In this Review, we describe the current evidence supporting the use of targeted therapies in patients with G/GEJ cancers and provide guidance on future research directions.

Lifestyles, genetics, and future perspectives on gastric cancer in east Asian populations

The prevalence of gastric cancer (GC) differs among regions worldwide, with the highest occurrence in east Asia. Thus, its etiology, with respect to ethnic background, environmental factors, and lifestyles, is also thought to differ essentially. In addition, etiology of GC is speculated to be changing due to the recent decrease in the Helicobacter pylori (H. pylori) infection in Japan. State-of-the-art somatic/germline cancer genomics has clarified the etiologies of gastric carcinogenesis. In this review article, we summarize past and present milestones in our understanding of GC achieved through genomic approaches, including a recent report that revealed higher-than-expected frequencies of GCs attributed to east Asian-specific germline variants in ALDH2 or CDH1 in combination with lifestyles. Based on this updated knowledge, we also discuss the possible impact of and high-risk approaches for GCs in the upcoming "H. pylori-negative era."

Helicobacter pylori and Gastric Cancer

Helicobacter pylori is present in approximately one-half of the world's population. There are significant differences in prevalence based on region, age, race/ethnicity, and socioeconomic status. H pylori is the most common cause of infection-related cancers. Studies have demonstrated the relationship between H pylori infection and gastric adenocarcinoma and mucosa-associated lymphoid tissue lymphoma. H pylori has features and enzymatic properties allowing it to survive in the acidic stomach environment, and has specific virulence factors that promote an increased risk of gastric pathology. Eradication of H pylori is first-line therapy for mucosa-associated lymphoid tissue lymphoma and decreases the risk of gastric adenocarcinoma.

Identification of Novel Alternative Splicing Events Associated With Tumorigenesis, Protein Modification, and Immune Microenvironment in Early-Onset Gastric Cancer

Background

Alternative splicing (AS), e.g. the tandem alternative polyadenylation (TAPA), has emerged as major post-transcriptional modification events in human disease. However, the roles of the AS and TAPA in early-onset gastric cancer (EOGC) have not been revealed.

Methods

The global AS profiles of 80 EOGC patients were analyzed. The EOGC-specific AS events (ESASs) were identified in both the EOGC and adjacent non-tumor tissues. The functional enrichment analysis, Splicing network, Alternative Polyadenylation (APA) core factor network, and cell abundancy analysis were performed. Furthermore, the landscapes of the AS events in the varied subtypes of the EOGC patients were evaluated.

Results

Overall, 66,075 AS events and 267 ESASs were identified in the EOGC. Furthermore, 4809 genes and 6152 gene isoforms were found to be aberrantly expressed in the EOGC. The Gene Ontology (GO) and Kyoto Encyclopedia of Gene and Genome (KEGG) pathway analyses showed that the significant pathway alterations might exist in these AS events, genes, and gene isoforms. Moreover, the Protein-protein interaction (PPI) network analysis revealed that the UBC, NEK2, EPHB2, and DCTN1 genes were the hub genes in the AS events in the EOGC. The immune cell infiltration analysis indicated a correlation between the AS events and the cancer immune microenvironment. The distribution of the AS events in varied EOGC subtypes, protein phosphorylation and glycosylation was uneven.

Conclusion

The study highlighted the vital roles of the AS in the EOGC, including modulating the specific protein modification and reshaping the cancer immune microenvironment, and yielded new insights into the diagnosis of the EOGC as well as cancer treatment.

In vivo CRISPR-Cas9 knockout screening using quantitative PCR identifies thymosin beta-4 X-linked that promotes diffuse-type gastric cancer metastasis

Gastric cancer (GC) is histologically classified into intestinal-type gastric cancer (IGC) and diffuse-type gastric cancer (DGC), and the latter is poorly differentiated and highly metastatic. In this study, using quantitative real-time polymerase chain reaction, we described a complete protocol for in vivo CRISPR-Cas9-based knockout screening of essential genes for DGC metastasis. We functionally screened 30 candidate genes using our mouse DGC models lacking Smad4, p53, and E-cadherin. Pooled knockout mouse DGC cells were transplanted into a spleen of syngeneic immunocompetent mice to study clonal advantages in context of a complex process of liver metastasis. Tmsb4x (thymosin beta-4 X-linked), Hmox1, Ifitm3, Ldhb, and Itgb7 were identified as strong candidate genes that promote metastasis. In particular, Tmsb4x enhanced DGC metastasis and stomach organoid-generated tumor growth in in vivo transplantation models. Tmsb4x promoted tumor clonogenicity and anoikis resistance. In situ hybridization analysis showed that Tmsb4x is highly expressed in E-cadherin-negative mouse DGC models compared with mouse IGC and intestinal cancer models. E-cadherin deficiency also increased Tmsb4x expression in stomach organoids via Wnt signaling activation. Collectively, these results demonstrate that Tmsb4x promotes DGC metastasis. In addition, this experimental system will aid in the identification of novel target genes responsible for DGC metastasis.

Differences in Somatic Mutation Profiles between Korean Gastric Cancer and Gastric Adenoma Patients

BACKGROUND

We aimed to investigate molecular factors potentially related to the progression of gastric adenoma (GA) to gastric cancer (GC) and compare the mutation characteristics between GC and GA.

METHODS

We conducted custom gene panel sequencing for 135 GC-related genes and estimated the difference in somatic mutation profiles between 20 GC and 20 GA cases.

RESULTS

A total of 31 somatic mutations, including 22 missense, 3 nonsense, and 6 frameshift mutations, were detected in 17 samples. We estimated an average of 1.8 mutations per sample (range, 1 to 3 mutations), with 12 in GC and 5 in GA. GC tended to have one or more mutated genes (p = 0.0217), as well as higher allele frequencies of mutated genes (p = 0.0003), compared to GA. Likewise, known driver mutations associated with GC tumorigenesis (TP53, ERBB2, PIK3CA, and RNF43) were identified in half of the GC cases (50%, 10/20; p = 0.0002). Only the mutant burden, regardless of gene type, was retained, with an odds ratio of 1.8392 (95% confidence interval (CI), 1.0071 to 3.3588; p = 0.0474).

CONCLUSION

Our study demonstrates that the accumulation of mutant burden contributes to tumorigenesis progression from GA to GC in Korean patients, regardless of the kind of genes. These findings may elucidate the molecular pathogenesis of gastric carcinogenesis and malignant progression.

Identified a disintegrin and metalloproteinase with thrombospondin motifs 6 serve as a novel gastric cancer prognostic biomarker by bioinformatics analysis

Objective: We aimed to explore the prognostic value of a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS) genes in gastric cancer (GC). Methods: The RNA-sequencing (RNA-seq) expression data for 351 GC patients and other relevant clinical data were acquired from The Cancer Genome Atlas (TCGA). Survival analysis and a genome-wide gene set enrichment analysis (GSEA) were performed to define the underlying molecular value of the ADAMTS genes in GC development. Besides, qRT-PCR and immunohistochemistry were all employed to validate the relationship between the expression of these genes and GC patient prognosis. Results: The Log rank test with both Cox regression and Kaplan–Meier survival analyses showed that ADAMTS6 expression profile correlated with the GC patients clinical outcome. Patients with a high expression of ADAMTS6 were associated with poor overall survival (OS). Comprehensive survival analysis of the ADAMTS genes suggests that ADAMTS6 might be an independent predictive factor for the OS in patients with GC. Besides, GSEA demonstrated that ADAMTS6 might be involved in multiple biological processes and pathways, such as the vascular endothelial growth factor A (VEGFA), kirsten rat sarcoma viral oncogene (KRAS), tumor protein P53, c-Jun N-terminal kinase (JNK), cadherin (CDH1) or tumor necrosis factor (TNF) pathways. It was also confirmed by immunohistochemistry and qRT-PCR that ADAMTS6 is highly expressed in GC, which may be related to the prognosis of GC patients. Conclusion: In summary, our study demonstrated that ADAMTS6 gene could be used as a potential molecular marker for GC prognosis.

Bioinformatics analysis for the identification of differentially expressed genes and related signaling pathways in H. pylori-CagA transfected gastric cancer cells

Aim

Helicobacter pylori cytotoxin-associated protein A (CagA) is an important virulence factor known to induce gastric cancer development. However, the cause and the underlying molecular events of CagA induction remain unclear. Here, we applied integrated bioinformatics to identify the key genes involved in the process of CagA-induced gastric epithelial cell inflammation and can ceration to comprehend the potential molecular mechanisms involved.

Materials and Methods

AGS cells were transected with pcDNA3.1 and pcDNA3.1::CagA for 24 h. The transfected cells were subjected to transcriptome sequencing to obtain the expressed genes. Differentially expressed genes (DEG) with adjusted P value < 0.05, — logFC —> 2 were screened, and the R package was applied for gene ontology (GO) enrichment and the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis. The differential gene protein–protein interaction (PPI) network was constructed using the STRING Cytoscape application, which conducted visual analysis to create the key function networks and identify the key genes. Next, the Kaplan–Meier plotter survival analysis tool was employed to analyze the survival of the key genes derived from the PPI network. Further analysis of the key gene expressions in gastric cancer and normal tissues were performed based on The Cancer Genome Atlas (TCGA) database and RT-qPCR verification.

Results

After transfection of AGS cells, the cell morphology changes in a hummingbird shape and causes the level of CagA phosphorylation to increase. Transcriptomics identified 6882 DEG, of which 4052 were upregulated and 2830 were downregulated, among which q-value < 0.05, FC > 2, and FC under the condition of ≤2. Accordingly, 1062 DEG were screened, of which 594 were upregulated and 468 were downregulated. The DEG participated in a total of 151 biological processes, 56 cell components, and 40 molecular functions. The KEGG pathway analysis revealed that the DEG were involved in 21 pathways. The PPI network analysis revealed three highly interconnected clusters. In addition, 30 DEG with the highest degree were analyzed in the TCGA database. As a result, 12 DEG were found to be highly expressed in gastric cancer, while seven DEG were related to the poor prognosis of gastric cancer. RT-qPCR verification results showed that Helicobacter pylori CagA caused up-regulation of BPTF, caspase3, CDH1, CTNNB1, and POLR2A expression.

Conclusion

The current comprehensive analysis provides new insights for exploring the effect of CagA in human gastric cancer, which could help us understand the molecular mechanism underlying the occurrence and development of gastric cancer caused by Helicobacter pylori.

Morphologic and molecular analysis of early-onset gastric cancer

BACKGROUND

Evidence suggests that early-onset gastric cancers are distinct from traditional gastric cancers; however, detailed genomic and morphologic characterization of these cancers has not been performed.

METHODS

Genomic analysis was performed for 81 patients with gastric cancer who were 50 years old or younger; pathology slides were available for 53 of these patients, and they were re-reviewed to perform a morphologic-molecular correlation analysis. The results were compared with corresponding cBioPortal data and The Cancer Genome Atlas (TCGA) analysis, which represent traditional gastric cancers. The TP53 molecular signature was established to determine the pattern of somatic mutational damage. Variants of potential germline origin were also identified from next-generation sequencing data.

RESULTS

A higher rate of CDH1 mutations (22.2% of early-onset gastric cancers vs 11.4% of traditional gastric cancers; P = .0042) but a similar rate of TP53 mutations (63% of early-onset gastric cancers vs 56.6% of traditional gastric cancers; P = .2674) were seen in early-onset cancers in comparison with traditional gastric cancers. The diffuse/mixed types correlated with the TCGA genomically stable type, and the remaining Lauren types correlated with the TCGA chromosomal instability type. Diffuse and indeterminate histologic types (overall survival, 26.25 months for the intestinal type, 20.5 months for the mixed type, 12.62 months for the diffuse type, and 9 months for the indeterminate type; P = .027) and the presence of a CDH1 gene mutation (overall survival, 9 months for mutant CDH1 and 22 months for wild-type CDH1; P = .013) significantly correlated with worse survival. The TP53 gene frequently showed transition mutations (65.5%) involving the CpG sites (49%). Variants of potential germline origin were seen in high-penetrance genes (CDH1 and APC) and moderate-penetrance genes (ATM, NBN, and MUTYH) in 9.9% of cancers.

CONCLUSIONS

Early-onset gastric cancer has distinct genomic alterations, such as CDH1 mutations, but shares with traditional gastric cancers a high frequency of TP53 mutations and the TP53 mutagenic signature. Diffuse and indeterminate histologic types and the presence of a CDH1 mutation are associated with worse overall survival. Endogenous factors leading to cytosine deamination and potential germline alterations in moderate-penetrance cancer susceptibility genes may be implicated in the pathogenesis of these cancers.

A novel genomic classification system of gastric cancer via integrating multidimensional genomic characteristics

BACKGROUND

Gastric cancer (GC) is one of the leading causes of cancer deaths with high heterogeneity. There is currently a paucity of clinically applicable molecular classification system to guide precise medicine.

METHODS

A total of 70 Chinese patients with GC were included in this study and whole-exome sequencing was performed. Unsupervised clustering was undertaken to identify genomic subgroups, based on mutational signature, copy number variation, neoantigen, clonality, and essential genomic alterations. Subgroups were characterized by clinicopathological factors, molecular features, and prognosis.

RESULTS

We identified 32 significantly mutated genes (SMGs), including TP53, ARID1A, PIK3CA, CDH1, and RHOA. Of these, PREX2, PIEZO1, and FSIP2 have not been previously reported in GC. Using a novel genome-based classification method that integrated multidimensional genomic features, we categorized GC into four subtypes with distinct clinical phenotypes and prognosis. Subtype 1, which was predominantly Lauren intestinal type, harbored recurrent TP53 mutation and ERBB2 amplification, high tumor mutation burden (TMB)/tumor neoantigen burden (TNB), and intratumoral heterogeneity, with a liver metastasis tendency. Subtype 2 tended to occur at an elder age, accompanying with frequent TP53 and SYNE1 mutations, high TMB/TNB, and was associated with poor prognosis. Subtype 3 and subtype 4 included patients with mainly diffuse/mixed type tumors, high frequency of peritoneal metastasis, and genomical stability, whereas subtype 4 was associated with a favorable prognosis.

CONCLUSIONS

By integrating multidimensional genomic characteristics, we proposed a novel genomic classification system of GC associated with clinical phenotypes and provided a new insight to facilitate genome-guided risk stratification and disease management.

Comparison of metastasis between early-onset and late-onset gastric signet ring cell carcinoma

Background

There is little knowledge to date about the distant metastasis of early-onset gastric signet ring cell carcinoma (SRCC) or the difference in metastasis based on age. Therefore, we conducted a comprehensive retrospective study using the Surveillance, Epidemiology, and End Results (SEER) database and data from our hospital.

Methods

Patients were collected from the SEER database and our hospital. Univariate and multivariate logistic regression analyses and propensity score matching (PSM) were used to identify risk factors for metastasis. K-M survival curves were generated to analyse patient survival.

Results

In total, we retrieved 2052 EOGC patients diagnosed with SRCC from the SEER database and included 403 patients from our hospital. K-M survival curves showed that late-onset SRCC patients had worse survival than early-onset patients but that late-onset SRCC patients were less likely to have distant metastasis, as validated by SEER data (OR = 0.462, 95%CI, 0.272–0.787; P = 0.004) and our data (OR = 0.301, 95%CI, 0.135–0.672; P = 0.003). Multivariate logistic regression and PSM analysis revealed that age of 45 or younger was an independent risk factor for distant metastasis.

Conclusion

Our study showed that distant metastasis was more common in early-onset SRCC than in late-onset SRCC. However, further studies are needed to explore the potential aetiologic basis for this disparity.

Genetic alterations and expression characteristics of ARID1A impact tumor immune contexture and survival in early-onset gastric cancer

The AT-rich Interactive Domain 1A (ARID1A) is one of the most frequently mutated genes in gastric cancer. Here, we found that genetic variants in noncoding regions of ARID1A associated with altered protein levels by target sequencing. Notably, tumors with ARID1A variants in the 3'untranslated region (3'UTR) exhibited remarkably increased heterogeneity of ARID1A protein. In general, genetic variants and protein deficiency of ARID1A in tumors were associated with a better survival. Strikingly, altered patterns and heterogeneity of ARID1A protein expression were observed in peritumor tissues and carried significant implications in defining tumor immune contexture by multiplex immunohistochemistry. By analyzing the spatial distribution of TILs, we showed that reduced ARID1A protein levels in both tumor and peritumor tissues were significantly correlated with increased density and proximity of TILs to tumor cells. In contrast, high heterogeneity of ARID1A expression was associated with increased TIL density, but reduced proximity of TILs to tumor cells. Collectively, our study characterized ARID1A genetic alterations and its protein expression patterns in EOGC, demonstrating new strategies for clinically assessing its molecular impact on tumor onset and progression, tumor immune response, and patient survival.