Microsatellite Instability In Gastric Cancer Research Articles

Abstract 1446: Gastric cancer with microsatellite instability: Ex vivo generation of syngeneic mouse models

Abstract The DNA mismatch repair (MMR) system is a highly conserved pathway crucial for maintaining the genomic integrity. MMR impairment in sporadic tumors is due to MLH1 epigenetic silencing or mutations in other MMR genes (such as MSH2, MSH6, PMS2) and leads to microsatellite instability (MSI). Two independent molecular classifications reported the existence of a MSI subgroup in gastric cancer (GC), including 22-23% of all cases. GC MSI inter and intra-tumoral heterogeneity represents a significant challenge for precise patient stratification and treatment. Even if MSI status in GC is usually associated with a good prognosis, some reports described a subpopulation of MSI GC patients displaying a worse outcome. Moreover, while clinical trials testing immune checkpoint inhibitors in MSI tumors showed effectiveness across all treatment lines, the outcomes in GC patients were not as remarkable as in other cancer types. From the analysis of MSI GC patients enrolled in phase III clinical trials testing anti-PD1 monotherapy, it emerged that nearly half of the tumors are intrinsically resistant and complete and long-lasting responses are achieved in very few cases. Tumor mouse immunocompetent models allow to mimic the complex interactions between a fully functional immune system and a developing tumor. MSI GC syngeneic mouse models could thus represent a valuable tool to better understand the molecular complexity and predict the clinical behavior of this subgroup. To obtain MSI GC mouse models, we generated non-transformed organoids from normal gastric mucosa of BALB/c mice as a starting point for the induction of a neoplastic transformation ex vivo. To induce MMR deficiency, we inactivated either Mlh1 or Msh2 genes using CRISPR/Cas9 genome editing. Importantly, we did not introduce any other alteration in known oncogenes and tumor suppressor genes, thus allowing the natural emergence of driver mutations in the context of the genetic instability. Over time, MMR deficient models, but not the WT controls, exhibited MSI and increased their mutational burden. Furthermore, when cultured in stringent culture conditions (two-dimensional culture, growth factor deprivation), only MMR deficient cells generated tumor masses upon subcutaneous injection in immunodeficient NOD SCID mice. Importantly, cells retrieved from the tumor masses (n = 8) exhibited mutations in a relevant fraction of genes associated with the MSI subgroup by TCGA (21 out of 35) – including Kras, Arid1a, Erbb3 and Tpr53 – thus offering a good representation of the human MSI GC mutational landscape. Given the immunogenicity of the Cas9 protein, we finalized our models optimizing the genome editing protocol to avoid a persistent Cas9 expression. Cas9-free MMR deficient models were able to generate tumors in immunocompetent BALB/c mice, thus representing a valuable resource to investigate tumor development, progression and responses to immunotherapy in vivo. Citation Format: Daniela Conticelli, Gabriele Picco, Cristina Migliore, Claudia Orrù, Fabrizio Maina, Emanuela Boccuni, Simona Corso, Silvia Giordano. Gastric cancer with microsatellite instability: Ex vivo generation of syngeneic mouse models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1446.

Intratumoral and peritumoral CT-based radiomics for predicting the microsatellite instability in gastric cancer.

To investigate the value of intratumoral and peritumoral radiomics based on contrast-enhanced computer tomography (CECT) to preoperatively predict microsatellite instability (MSI) status in gastric cancer (GC) patients. A total of 189 GC patients, including 63 patients with MSI-high (MSI-H) and 126 patients with MSI-low/stable (MSI-L/S), were randomly divided into the training cohort and validation cohort. Intratumoral and 5-mm peritumoral regions' radiomics features were extracted from CECT images. The features were standardized by Z-score, and the Inter-andintraclass correlation coefficient, univariate logistic regression analysis, and least absolute shrinkage and selection operator (LASSO) were applied to select the optimal radiomics features. Radiomics scores (Rad-score) based on intratumoral regions, peritumoral regions, and intratumoral + 5-mm peritumoral regions were calculated by weighting the linear combination of the selected features with their respective coefficients to construct the intratumoral model, peritumoral model, and intratumoral + peritumoral model. Logistic regression was used to establish a combined model by combining clinical characteristics, CT semantic features, and Rad-score of intratumoral and peritumoral regions. Eleven radiomics features were selected to establish a radiomics intratumoral + peritumoral model. CT-measured tumor length and tumor location were independent risk factors for MSI status. The established combined model obtained the highest area under the receiver operating characteristic (ROC) curve (AUC) of 0.830 (95% CI, 0.727-0.906) in the validation cohort. The calibration curve and decision curve demonstrated its good model fitness and clinical application value. The combined model based on intratumoral and peritumoral CECT radiomics features and clinical factors can predict the MSI status of GS with moderate accuracy before surgery, which helps formulate personalized treatment strategies.

Low incidence of microsatellite instability in gastric cancers and its association with the clinicopathological characteristics: a comparative study

Gastric cancer is a complex heterogeneous disease with different molecular subtypes that have clinical implications. It is characterized by high mortality rates and limited effective therapies. Microsatellite instability (MSI) has been recognized as a subgroup with a good prognosis based on TCGA and ACRG categorizations. Besides its prognostic and predictive value, gastric cancers with high MSI exhibit different clinical behaviors. The prevalence of high MSI has been assessed in gastric cancer worldwide, especially in East Asia, but there is a lack of such information in the Middle East. Therefore, this study aimed to investigate the incidence and status of MSI in Iranian gastric cancer patients using 53 samples collected from 2015 to 2020 at Taleghani Hospital Medical Center. DNA from tumoral and normal tissues were extracted and assessed through multiplex-PCR based on five mononucleotide repeats panel. Clinicopathological variables, including age, sex, Lauren classification, lymph node involvement, TNM stage, differentiation, localization, and tumor size, were also analyzed. With 2 males and 2 females, high microsatellite instability represented a small subgroup of almost 7.5% of the samples with a median age of 60.5 years. High microsatellite instability phenotypes were significantly associated with patients aged 68 years and older (p‑value of 0.0015) and lower lymph node involvement (p‑value of 0.0004). Microsatellite instability was also more frequent in females, with distal gastric location, bigger tumor size, and in the intestinal type of gastric cancer rather than the diffuse type.

Microsatellite instability in gastric cancer: An institutional case series analysis in patients treated with neoadjuvant therapy

IntroductionPast studies documented that microsatellite instability (MSI) is associated with improved survival in gastric cancer (GC). The aim of this study was to evaluate MSI status in a series of GCs treated with neoadjuvant therapy in relation to the tumors' characteristics and oncological outcomes. MethodsPatients with GCs treated between 2017 and 2022 ​at a single Italian high-volume Institution undergoing pre-operative treatment followed by resection were included if studied for their microsatellite status. Clinicopathological data were analyzed for the association with MSI. The same features were analyzing pooling the series with a subset of patients from another European trial.Secondary outcomes included the overall (OS), and disease-free (DFS) survivals comparing MSI vs microsatellite stable (MSS) GCs, and GCs presenting complete-major response (TRG1-2) vs partial response (TRG3-4) and absence of response (TRG5). ResultsAmong 73 patients selected, 12.3% were MSI. In the single institutional analysis, we documented a difference in the distribution of ypT stages with a prevalence of ypT0 patients in MSI vs MSS patients (ypT0 respectively 11.1% vs 1.6%, p ​< ​0.0001). However, this difference was not of statistical value when pooling patients with those from the European trial (overall 108 patients, 9.2% MSI; ypT0 respectively 10.0% vs 2.0%, p 0.144). In the pooled analysis, a prevalence of female patients was reported in the MSI group comparing MSS (respectively, 70.0% vs 27.6%, p 0.01). At a mean follow-up of 27.7 months, OS and DFS survivals were reported similar comparing MSS and MSI (log-rank test respectively p 0.18 and p 0.96), however TRG1-2 ​GCs had improved OS and DFS comparing other sub-groups (TRG1-2 vs TRG3-4 vs TRG5, OS and DFS log-rank test respectively p 0.017 and p 0.0029). ConclusionThis study could not demonstrate a correlation between microsatellite status and survival in gastric cancer patients who underwent pre-operative treatment. A complete/major response was the only variable correlated with mid-term survival.

Identification of RNF150 as the hub gene associated with microsatellite instability in gastric cancer

Gastric cancer (GC) is a common digestive tract malignancy with the sixth global incidence and third cancer-related deaths, respectively. Microsatellite instability (MSI), accounting for one of the molecular subtypes of GC, plays an important role in GC and is affected by a sophisticated network of gene interactions. In this study, we aimed to explore the expression pattern and clinical performance of MSI related gene in GC patients. Weighted gene co-expression network analysis (WGCNA) was exploited to single out the vital module and core genes in TCGA database. We applied the protein–protein interaction (PPI) and survival analysis to propose and confirm RNF150 as the hub gene in GC. Finally, we utilized immunohistochemistry (IHC) and reverse transcription-polymerase chain reaction (RT-PCR) to explore the expression pattern of RNF150 in GC patients. With the highest weight correlation and standard correlation, RNF150 was selected as the hub gene for following validation. In validation, data obtained from the test sets showed a lower expression of RNF150 in MSI GC compared to microsatellite stability (MSS) GC. Moreover, survival analysis shows that MSI GC patients with a lower RNF150 expression level displayed the longer OS time. Compared to the expression in normal gastric tissues, the protein level of RNF150 was virtually up-regulated in ten cases of GC tissues. Furthermore, RNF150 protein level was decreased in MSI GC samples compared to MSS GC samples. When validated the mRNA expression with RT-PCR in fresh GC tissues, we also found the similar trend. RNF150 was identified as a novel MSI-related gene in GC. It is expected to be an auspicious prognostic biomarker for GC patients.

A virtual biopsy study of microsatellite instability in gastric cancer based on deep learning radiomics

ObjectivesThis study aims to develop and validate a virtual biopsy model to predict microsatellite instability (MSI) status in preoperative gastric cancer (GC) patients based on clinical information and the radiomics of deep learning algorithms.MethodsA total of 223 GC patients with MSI status detected by postoperative immunohistochemical staining (IHC) were retrospectively recruited and randomly assigned to the training (n = 167) and testing (n = 56) sets in a 3:1 ratio. In the training set, 982 high-throughput radiomic features were extracted from preoperative abdominal dynamic contrast-enhanced CT (CECT) and screened. According to the deep learning multilayer perceptron (MLP), 15 optimal features were optimized to establish the radiomic feature score (Rad-score), and LASSO regression was used to screen out clinically independent predictors. Based on logistic regression, the Rad-score and clinically independent predictors were integrated to build the clinical radiomics model and visualized as a nomogram and independently verified in the testing set. The performance and clinical applicability of hybrid model in identifying MSI status were evaluated by the area under the receiver operating characteristic (AUC) curve, calibration curve, and decision curve (DCA).ResultsThe AUCs of the clinical image model in training set and testing set were 0.883 [95% CI: 0.822–0.945] and 0.802 [95% CI: 0.666–0.937], respectively. This hybrid model showed good consistency in the calibration curve and clinical applicability in the DCA curve, respectively.ConclusionsUsing preoperative imaging and clinical information, we developed a deep-learning-based radiomics model for the non-invasive evaluation of MSI in GC patients. This model maybe can potentially support clinical treatment decision making for GC patients.Graphical abstract

Does Epstein-Barr virus-positive gastric cancer establish a significant relationship with the multiple genes related to gastric carcinogenesis?

Gastric cancer has been categorized into molecular subtypes including Epstein-Barr virus (EBV)-positive tumors, which provide clinicopathological and prognostic information. In this study, we investigated the EBV infection status of patients with gastric cancer and its correlation with the clinicopathological characteristics and multiple genes related to gastric carcinogenesis. The data of 460 gastric cancer patients who underwent curative gastrectomy with D2 lymph node dissection between January 2017 and February 2022 were analyzed. The clinicopathological features and prognosis of the patients with EBV-positive gastric cancers were compared with those of EBV-negative gastric cancers. Immunohistochemistry for epidermal growth factor receptor (EGFR), C-erb B2, Ki-67, and p53 was performed. Additionally, in situ hybridization was conducted to detect EBV, and microsatellite instability (MSI) analysis was used to assess the deficiency in mismatch repair (MMR) genes. EBV-positivity and MSI were identified in 10.4% and 37.3% of gastric cancer patients, respectively. EBV positivity was associated with male gender (P = 0.001), proximal location (P = 0.004), poorly differentiated histological type (P = 0.048), moderate to severe lymphoid stroma (P = 0.006), high Ki-67 expression (P = 0.02), and a shorter resection margin. EGFR was more often expressed in EBV-negative gastric cancers (P < 0.001). MSI tumors were associated with older age (P = 0.01), the presence of lymphatic invasion (P = 0.02), less perineural invasion (P = 0.05), and the presence of H. pylori infection (P = 0.05). EBV positive gastric cancer is associated with increased Ki-67 and decreased EGFR expression and a shorter resection margin due to the prominent lymphoid stroma. However, MMR deficiency is not associated with EBV status even though MSI gastric cancer is related to H. pylori status.

Performance of Immunohistochemical and Molecular Methods in Detecting Microsatellite Instability in Gastric Cancer: A Multicenter Study

Introduction: Microsatellite instability (MSI) is an important prognostic molecular biomarker for gastric cancer (GC). MSI status may be detected by immunohistochemistry (IHC) for mismatch repair (MMR) proteins and polymerase chain reaction (PCR). Idylla™ MSI assay has not been validated for GC but may prove to be a valid alternative. Methods: In a series of 140 GC cases, MSI status was evaluated by IHC for MLH1, PMS2, MSH2, and MSH6; gold-standard pentaplex PCR panel (PPP) (BAT-25, BAT-26, NR-21, NR-24, and NR-27); and Idylla. Statistical analysis was performed using SPSS 27.0. Results: PPP identified 102 microsatellite stable (MSS) cases and 38 MSI-high cases. Only 3 cases showed discordant results. Compared with PPP, the sensitivity was 100% for IHC and 94.7% for Idylla. Specificity was 99% for IHC and 100% for Idylla. MLH1 IHC alone showed sensitivity and specificity of 97.4% and 98.0%, respectively. IHC identified three indeterminate cases; all were MSS according to PPP and Idylla. Conclusion: IHC for MMR proteins represents an optimal screening tool for MSI status in GC. If resources are limited, isolated MLH1 evaluation may constitute a valuable option for preliminary screening. Idylla may help detect rare MSS cases with MMR-loss and define MSI status in indeterminate cases.

High Frequency of Microsatellite Instability among Non-Metastatic Gastric Cancer.

Background: Microsatellite instability (MSI) is considered a key factor in carcinogenesis and a genetic alteration pattern in many types of cancers such as gastric cancer (GC). Although the role of MSI in colorectal cancer (CRC) is well known, its prognostic impact on GC has not been clearly defined. The assessment of MSI in GC has notbeen documented in the Iranian population yet. Therefore, this study analyzed the association of MSI status with GC in Iranian patients. Materials and Methods: We compared the frequency of MSI at 5 loci from formalin-fixed paraffin-embedded (FFPE) gastrectomy specimens, between metastatic and non-metastatic cases of GC (N = 60). A panel of five quasi-monomorphic markers and a single dinucleotide marker with linker-based fluorescent primers was used. Results: MSI was observed in 46.6% of cases, including MSI-high (H) (33.3%) and MSI-Low (L) (13.3%). Moreover, the most unstable and stable markers in our study were NR-21 and BAT-26 accordingly. MSI-H and MSI were seen more frequently in non-metastatic tumors (p= 0.028 and p= 0.019, respectively). Conclusion: The current study showed MSI status more frequently in non-metastatic GC which may reflect a good prognostic factor in GC like CRC. Although, larger and more comprehensive studies are needed to confirm this statement. A panel consisting of NR-21, BAT-25, and NR-27 mononucleotide markers appears to be reliable and useful markers for detecting MSI in GC in Iranian patients.

Lifestyle and Dietary Factors Causing Microsatellite Instability Gastric Cancer Detected using Ensemble Modeling

Aim of this study is to identify diet and lifestyle patterns that cause microsatellite instability gastric cancer (MSI-GC) using supervised machine learning algorithms. There were 142 genetic variants acquired via targeted resequencing of 60 biomarker genes from gastric tumor samples and tabulated with respect to MSI status, diet and lifestyle characteristics. Four classifiers (logistic regression, random forest, logistic regression, multilayer perceptron) were used to train the data and evaluated based on their classification efficiency. Data analysis revealed features extracted using ridge regression: extra salt, smoked food, smokeless tobacco products (Khaini /sadha), alcohol and betel nut leaf with lime (khuva) were the core factors for causing MSI-GC. The extracted features were exploited using random forest and multilayer perceptron classifiers, which has produced accuracy, precision, recall, F1 score, and Receiver operating characteristics (ROC) curve of 96 %. The brier score was 0.04 and Matthews correlation coefficient (MCC) was +0.91. Linear regression results revealed khuva was main driving factor and extra salt, smoked food, khaini/sadha and alcohol were confounding factors to cause MSI-GC. This is a first-time report that integrates mutation and diet-lifestyle data using machine learning, to precisely identify the driving and confounding factors for causing MSI-GC.

Gastric cancer with microsatellite instability displays increased thymidylate synthase expression.

Gastric cancer (GC) with microsatellite instability (MSI) is a less aggressive disease and associated with resistance to 5-fluorouracil (5-FU)-based chemotherapy (CMT). Thymidylate synthase (TS) is inhibited by 5-FU, and another potential mediator of therapeutic resistance to 5-FU. Therefore, we aimed to analyze the association between MSI and TS expression in GC, and its impact on disease outcomes. We retrospectively evaluated GC who underwent D2-gastrectomy. MSI and TS were analyzed by immunohistochemistry. We also investigated p53 expression, PD-L1 status, and tumor-infiltrating lymphocytes (CD4and CD8). Out of 284 GC, 60 (21.1%) were MSI. Median TS-score for all cases was 16.5. TS expression was significantly higher in MSI compared to microsatellite-stable (MSS;p < 0.001). Considering both status, GC were classified in four groups: 167 (58.8%) MSS + TS-low; 57 (20.1%) MSS + TS-High; 24 (8.5%) MSI + TS-low; and 36 (12.7%) MSI + TS-high. MSI + TS-high group had less advanced pTNM stage, higher CD8+T cells levels (p < 0.001) and PD-L1 positivity (p < 0.001). Normal p53 expression was related to MSI GC (p < 0.001). Improved survival was observed in MSI + TS-high, but no survival benefit was seen with CMT. MSI GC was associated with high TS levels, which may explain therapeutic resistance to 5-FU. Additionally, MSI + TS-high showed better survival, but without improvement with CMT.

The Influence of Heavy Metals on Gastric Tumorigenesis.

Objectives This study aimed to observe the relationship among heavy metals concentration, microsatellite instability (MSI), and human epidermal growth factor receptor type 2 (HER2) gene amplification in gastric cancer (GC) patients. Methods The concentrations of 18 heavy metals in the plasma of GC patients and healthy controls were measured by inductive coupled plasma emission spectrometry (ICP-MS). MSI detection was conducted by detecting 5 microsatellite repeat markers by PCR analysis. HER2 gene amplification was detected by fluorescence in situ hybridization (FISH). The relationship among heavy metal elements, tumor biomarkers, HER2 amplification, and MSI status was analyzed by Pearson correlation analysis. Results A total of 105 GC patients and 62 healthy controls were recruited in this study. The concentration of arsenic (As), chromium (Cr), cuprum (Cu), mercury (Hg), manganese (Mn), lead (Pb), stibium (Sb), selenium (Se), stannum (Sn), strontium (Sr), thallium (Tl), vanadium (V), and zinc (Zn) were significantly different between GC patients and controls. Among 105 GC patients, including 87 microsatellite-stable (MSS) samples and 18 MSI samples, the concentration of Ga is significantly higher in the MSI group than that in the MSS group. Meanwhile, in 97 GC patients having detected HER2 gene amplification, 69 of 97 had negative HER2 gene amplification and the rest 28 GC patients had positive HER2 gene amplification. The concentration of Hg, Sn, and Tl is noticeably higher in the HER2 positive group than in the HER2 negative group. Only Sb was positively correlated with MSI, but none of these heavy metals was correlated with HER2 gene amplification. Conclusions The results indicated that Sb has significant positive correlation with the MSI status, which suggests that Sb may cause MSI in GC. However, further research studies are required to elucidate the mechanisms in the near feature.

Microsatellite instability in gastric cancer is a predictor of a favorable prognosis

Evaluation of the frequency of microsatellite instability in gastric adenocarcinomas in patients of the Russian Federation, determination of the relationship of microsatellite instability with clinical and morphological characteristics and the impact on the prognosis. We used samples of surgical material from 310 patients with a verified diagnosis of gastric cancer. The age of the patients ranged from 22 to 85 years (mean 63 years). The median follow-up of patients was 83 months. Each sample was immunohistochemically stained with antibodies to microsatellite instability markers MLH1, MSH2, MSH6, and PMS2. The results were compared with the main clinical and morphological characteristics of gastric cancer and data on patient survival. The frequency of detection of MMR-negative tumors in the Russian population is 8.1% of all patients with gastric cancer. It was found that patients with MMR-negative gastric carcinomas are older (mean age 69 years, p=0.008). In this group predominates distal localization of tumors, type 2 according to R. Bormann classification (p=0.010), tubular histological type (p=0.010), intestinal subtype according to P. Lauren classification (p=0.003). There were no significant differences between MMR-negative and MMR-positive tumors in terms of other clinical and morphological parameters (including the stage of the tumor process). The overall median survival of patients with MMR-negative tumors was 76%, which significantly (p=0.013) exceeds that in the group of MMR-positive tumors (36%). It was found that despite significant differences in survival, MMR-status is not an significant prognostic factor in gastric cancer (HR=0.983). The established differences in patient survival make it possible to distinguish a group of MMR-negative tumors into a separate pathogenetic subtype of gastric cancer (MSI subtype) based on immunohistochemical studies. This subtype occurs predominantly in elderly patients with tubular gastric adenocarcinomas and is characterized by a favorable prognosis.

Microsatellite instability in Chinese gastric cancer and its correlation with clinical characteristics.

Microsatellite instability (MSI) remains a focus of interest in cancer research, but the characteristics of MSI in gastric cancer (GC) are ambiguous. In this retrospective study, we analyzed the prevalence of MSI and the expression of programmed death-ligand 1 (PD-L1) and cluster of differentiation 8 (CD8) cells in Chinese GC patients. A total of 393 GC patients admitted to two centers from January 2010 to December 2017 were enrolled. The prevalence of MSI in this cohort was 3.4% and most frequently occurred in females, patients aged between 59 and 69 years, and patients at a lower clinical stage. All MSI GCs had CD8 expression but lacked PD-L1 expression, indicating that MSI was related to CD8 expression but irrelevant to PD-L1 expression. However, there was no significant difference in the expression of CD8/PD-L1 between MSI GC and microsatellite stable (MSS) GC. Kaplan-Meier survival curves revealed that patients with MSI had a significantly longer overall survival (OS) than patients with MSS. In Chinese GC patients, MSI frequently occurred in females, patients aged between 59 and 69, and patients with lower clinical stages. Patients with MSI-High (MSI-H) and MSI-Low (MSI-L) had a longer OS than patients with MSS. MSI was related to CD8 expression but irrelevant to PD-L1 expression.

HNRNPL Is Identified and Validated as a Prognostic Biomarker Associated with Microsatellite Instability in Human Gastric Cancer.

Microsatellite instability (MSI) is emerging as a promising subtype related to immunotherapy in gastric cancer (GC). However, the underlying mechanism between MSI and microsatellite stability (MSS) remains unclear. In this study, we conducted a weighted gene co-expression network analysis and found that the expression of heterogeneous nuclear ribonucleoprotein L (HNRNPL) was significantly increased in MSI GC compared with MSS GC. This finding was further validated in public GC cohorts and commercialized human GC tissue microarray. The significant negative correlation with the expression of mismatch repair protein mutL homolog 1 (MLH1) may be one of the potential mechanisms for the upregulation of HNRNPL expression in MSI GC (R = -0.689, p = 8.59e-11). In addition, HNRNPL expression was markedly upregulated in GC tissues compared with adjacent normal tissues. High HNRNPL expression also predicted a poor prognosis in GC patients. Finally, gene set enrichment analysis revealed that high HNRNPL MSI GC samples were highly positive associated with the biological functions of inflammation and cell proliferation, such as interferon gamma response, MYC targets, E2F targets, and G2/M checkpoints. In conclusion, HNRNPL could be a new MSI-associated prognostic biomarker in GC and could be a new target for the MSI GC treatment.

Prognostic impact of microsatellite instability in gastric cancer.

Gastric cancer is a common and deadly cancer. Several factors are associated with its prognosis; however, controversy exists about the role of microsatellite instability (MSI). We aimed to determine the 5-year overall survival (OS) of MSI in gastric adenocarcinoma.A cross-sectional study was carried out on gastric adenocarcinoma in clinical stages I to III treated with D2 gastrectomy between 2010–2013. MSI was demonstrated by immunohistochemistry. We performed a survival analysis comparing cases with and without MSI.From 102 cases, 9.8% showed MSI. The median age was 63 years (range 33–91 years), and 57.8% were men. The more prevalent site of occurrence was the antrum (46.1%), 78.5% of the cases presented in stage III, 47.1% were of the diffuse type, 45.1% were of an intestinal type, and 7.8% were mixed. MSI cases were associated with lower clinical stages (stages I–II) and with better 5-year OS (100 vs. 47 months, p = 0.017). In a multivariate analysis, MSI was independently associated with better survival (HR = 0.209, 95% CI: 0.046–0.945, p = 0.042). MSI gastric cancers presented in early clinical stages and had favourable prognosis compared with non-MSI cancers.

Microsatellite instability in gastric carcinomas in Kano, Nigeria

Background and Objectives: Gastric carcinoma, though relatively less prevalent in most parts of Africa and Nigeria, usually presents at an advanced stage in most of our patients. This makes the elucidation of clinical and molecular factors relating to prognosis an important avenue to explore. Gastric carcinomas exhibiting microsatellite instability (MSI) are said to have better prognosis, but there has been no study in Northern Nigeria. We, therefore, undertook this study to evaluate the proportion of MSI gastric carcinoma in our center. Methodology: This retrospective 5-year study was done on 48 histologically diagnosed gastric carcinomas to evaluate the immunohistochemical expression of mismatch repair DNA proteins: MLH1 and MSH2. Results: Forty-eight gastric cancer (GC) biopsies fulfilled the study criteria. They were from patients aged 23–80 years, with a mean of 52.1 years (standard deviation [SD] ±12.79) and male to female ratio = 3.4:1. Twenty cases (42%) had MSI, with a mean age of 51.7 years (SD ± 12.75; P = 0.67). The remaining 28 cases were microsatellite stable (MSS), with a mean age of 53.3 years (SD ± 12.92). Male preponderance was more marked in the MSS group (6:1) than in the MSI group (2.3:1). Intestinal carcinoma was by far the most common histologic type in both MSI (75%) and MSS (70%) groups. Conclusion: Forty-two percent of gastric carcinomas were harboring MSI. Although our sample size was small, it nonetheless provided useful insight and baseline data for MSI gastric carcinoma in our center. MSI GC appears to be more common in our center than an earlier Southern Nigerian study. This is consistent with the widely differing proportion of MSI gastric carcinoma across the globe, sometimes within the same country. Further studies are therefore required to make sense of this seemingly conflicting data.

Gastric cancer molecular classification and adjuvant therapy: Is there a different benefit according to the subtype?

Gastric cancer (GC) has been defined in distinct molecular subtypes with different therapeutic implications. However, its clinical significance and prognosis regarding standard chemotherapy (CMT) remains unclear. This study aimed to analyze the impact of perioperative or adjuvant treatment among subtypes of GC. We retrospectively evaluated all stage II/III patients with GC who underwent a curative gastrectomy. Based on immunohistochemistry and in situ hybridization techniques, GC was classified into five subtypes: Epstein-Barr virus (EBV) positive, microsatellite instability (MSI), e-cadherin aberrant, p53-aberrant, and p53-normal. Among the 178 CG included, 111 patients received CMT and 67 were treated with surgery alone. Survival analysis showed that p53-aberrant GC treated with CMT had better disease-free survival (DFS) compared with surgery alone (P = .001).There was no significant difference in DFS between patients who received CMT and those with surgery alone for EBV, MSI, E-cadherin, and p53-normal GC. An improvement in overall survivalwas observed only for E-cadherin (P = .001) and p53-aberrant (P < .001) patients who received CMT. CMT showed different impact on the survival of CG according to the molecular subtype. No survival benefit was observed for EBV and MSI groups who received CMT. GC with p53-aberrant had a significant benefit in survival with standard therapy.

Abstract 1497: Identification of discrepancy between CTLA4 expression and CTLA4 activation in gastric cancer

Abstract Objective: Recently, immune checkpoints blockers showed higher anti-tumor activity for advanced gastric cancer (GC). The purpose of the study is to find out biomarkers related to anti-CTLA4 therapy. Materials and Methods: Datasets of GEO, TCGA and GESA were extracted. Differential expression of CTLA4 between cancer tissues and normal mucosa, enrichment of WT (wild type) vs CTLA4_KO (knockout) upregulated gene set and clinical significance were analyzed. The expression of CTLA4,CD3 and granzyme A (GZMA) were validated on 30 cases of Chinese GC. MSI marker MLH1 and EBV marker EBER were examined on 30 cases of Chinese GC by immunohistochemistry and in situ hybridization. Results: CTLA4 was up-regulated in GC tissue relative to normal mucosa in datasets of GSE27342 (fold change=1.586, P&amp;lt;0.001) and GSE63089 (fold change=1.365, P&amp;lt;0.001). Increased CTLA4 expression was positively related to CTLA4 activation. EBV-associated GC (EBVaGC) and microsatellite instability GC (MSIGC) disclosed higher CTLA4 levels than other GCs. Genomic stability GC (GSGC) also showed higher enrichment score of CTLA4 activation. CTLA4 activation resulted in shorter overall survival in GC. The expression level of CTLA4 was well correlated to GZMA (R=0.701, P&amp;lt;0.001) and CD3 (R=0.750, P&amp;lt;0.001). Conclusions: GSGC was firstly identified as the potential GC subtypes responsive to anti-CTLA4 treatment. Note: This abstract was not presented at the meeting. Citation Format: Yingyan Yu. Identification of discrepancy between CTLA4 expression and CTLA4 activation in gastric cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1497.

Correlation of CHAF1A with adjuvant chemotherapy outcome and microsatellite instability in gastric cancer.

e15511 Background: Clinical outcomes of adjuvant chemotherapy in gastric cancer (GC) have considerable stage-independent variability, which underscores the need for predictive molecular markers. Previous studies indicated that CHAF1A played a critical role in tumor growth, but whether it was associated with adjuvant chemotherapy in GC was still unknown. This retrospective study investigated the prognostic value of CHAF1A in adjuvant chemotherapy of GC. Methods: A total of 325 stage IB-III patients with fluoropyrimidines (FU)-based adjuvant chemotherapy after curative D2 gastrectomy meeting eligibility criteria were selected. CHAF1A protein expression was determined by immunohistochemical method. The primary outcomes were Overall survival (OS) and Disease-free survival (DFS). Kaplan-Meier method was used to estimate survival curve and Cox model for multifactor analysis. Results: CHAF1A mRNA was overexpressed in GC tissues and positive CHAF1A protein expression was not associated with OS and DFS in overall patients treated by FU-based chemotherapy ( P = 0.391 and 0.511, respectively). However, as stratified by tumor sites, positive CHAF1A expression was associated with poor OS and DFS in non-cardia cancer ( P = 0.009 and 0.007, respectively) but not in cardia cancer ( P = 0.229 and 0.112, respectively). Multivariate analysis indicated that CHAF1A expression level was still an independent predictor for both OS (HR = 2.42; 95% CI: 1.12-5.20; P = 0.024) and DFS (HR = 1.91; 95% CI: 1.03-3.54; P = 0.039) in non-cardia GC. Furthermore, CHAF1A was correlated with the status of microsatellite instability ( P = 0.025). Conclusions: CHAF1A might be a predictor for outcomes of FU-based adjuvant chemotherapy in patients with non-cardia GC, but needed further prospective studies to confirm.