Usefulness of Immunohistochemistry for Microsatellite Instability Screening in Gastric Cancer

How do I treat dMMR/MSI gastro-oesophageal adenocarcinoma in 2025? A position paper from the EORTC-GITCG gastro-esophageal task force

In less than a decade, immune checkpoint inhibitors (ICIs) have transformed the management of mismatch repair-deficient (dMMR) and microsatellite instability-high (MSI) cancers. However, beyond colorectal cancer (CRC), much of the evidence is mostly derived from non-randomized phase II studies or post-hoc analyses of broader clinical trials. dMMR/MSI tumours represent a specific subgroup of gastro-esophageal adenocarcinomas (GEA), accounting for approximately 9 % of cases, with a higher prevalence in early-stage compared to advanced-stage disease and older female patients. These tumours are predominantly sporadic, often linked to MLH1 promoter methylation, and rarely exhibit HER2 overexpression/ERBB2 amplification or other oncogenic drivers. The treatment landscape for early stage dMMR/MSI GEA is likely to change substantially soon, as ICIs have shown high pathological complete response (pCR) rates in small phase II trials, raising questions on optimisation of neoadjuvant therapy, and paving the way for organ preservation. The standard of treatment for untreated patients with advanced dMMR/MSI GEA is chemotherapy + ICI irrespectively of PDL-1 status. However, the role of chemotherapy-free regimen consisting of CTLA-4 plus PD-1 inhibitors remains undetermined. This review addresses these and other emerging questions, offering expert opinions and insights into the future therapeutic landscape for dMMR/MSI GEA.

Prognostic significance of microsatellite instability in patients with resectable gastric cancer

BACKGROUND

Microsatellite instability (MSI) gastric cancer (GC) generally has a better prognosis than microsatellite-stable (MSS) GC and has been associated with nonsurvival benefit with the addition of chemotherapy (CMT) compared with surgery alone. However, patients with MSI have distinct clinicopathological characteristics. This study aimed to compare the survival outcomes between patients with MSI GC and those with MSS GC. In addition, this study analyzed the survival outcomes of patients with MSI GC who received CMT.

METHODS

This study reviewed all patients with GC who underwent curative gastrectomy. Patients were divided into MSI group and the MSS group. Propensity score matching (PSM) was used to match clinicopathological factors.

RESULTS

Among the 378 patients enrolled, 78 (20.6%) had MSI. Older age (P < .001), subtotal gastrectomy (P = .008), pN0 (P = .020), and earlier pTNM stage (P = .012) were associated with MSI GC. Survival analysis showed better disease-free survival (DFS) and overall survival (OS) of patients in the MSI group (P = .012 and P = .019, respectively). After PSM, 78 patients were matched to each group. All variables assigned to the scores were well matched, and both groups became equivalent. After the matching, the differences in DFS and OS according to MSI/MSS status were estimated to be larger than before (DFS: 63.3% vs 41.4%; P = .002; OS: 65.8% vs 42.5%; P = .002). Regarding patients referred for CMT, there was no difference in DFS and OS between patients with MSI GC who underwent CMT and those who underwent surgery alone (P = .255 and P = .178, respectively).

CONCLUSION

Even after controlling for clinicopathological characteristics, MSI was identified as a prognostic factor for patient survival. MSI GC showed no significant survival benefit with the addition of CMT.

Creation of a Quality Payment Program Measure for Mismatch Repair or Microsatellite Instability Biomarker Testing Status in Colorectal, Endometrial, Gastroesophageal, or Small Bowel Carcinoma

CONTEXT.—

Quality measures that are supported by evidence-based clinical practice guidelines are preferred for assessing the quality of pathologists' practices. Careful testing of a measure ensures that scores obtained by that measure reflect the quality of a pathologist's practice.

OBJECTIVE.—

To specify a new quality measure and to demonstrate through testing that it is suitable for measuring pathologists' appropriate incorporation of information regarding microsatellite instability (MSI) and/or mismatch repair (MMR) status in pathology reports for colorectal, endometrial, gastroesophageal, and small bowel carcinoma.

DESIGN.—

The College of American Pathologists collaborated with the American Gastroenterological Association to specify and test the new measure. Face validity testing was used to investigate the validity of the measure. Feasibility testing was conducted to understand if data elements required by the measure specification were readily accessible. Signal-to-noise analysis was used to characterize the measure's reliability.

RESULTS.—

Guideline recommendations for MSI and/or MMR testing supported specifications for the measure. Face validity testing indicated that the measure could distinguish the quality of care provided. Data elements required by the measure specification were found to be accessible, which supported the measure's feasibility. Reliability testing showed that differences in measure score were attributable to real differences in performance rather than random variation in scoring.

CONCLUSIONS.—

The Mismatch Repair or Microsatellite Instability Biomarker Testing Status in Colorectal Carcinoma, Endometrial, Gastroesophageal, or Small Bowel Carcinoma measure was appropriately specified, and testing demonstrated that it is well suited for characterizing the quality of pathologists' communication of MMR and/or MSI status.

Mismatch Repair Deficiency Is a Prognostic Factor Predicting Good Survival of Opisthorchis viverrini-Associated Cholangiocarcinoma at Early Cancer Stage

BACKGROUND

The mismatch repair (MMR) system prevents DNA mutation; therefore, deficient MMR protein (dMMR) expression causes genetic alterations and microsatellite instability (MSI). dMMR is correlated with a good outcome and treatment response in various cancers; however, the situation remains ambiguous in cholangiocarcinoma (CCA). This study aims to evaluate the prevalence of dMMR and investigate the correlation with clinicopathological features and the survival of CCA patients after resection.

MATERIALS AND METHODS

Serum and tissues were collected from CCA patients who underwent resection from January 2005 to December 2017. Serum OV IgG was examined using ELISA. The expression of MMR proteins MLH1, MSH2, MSH6 and PMS2 was investigated by immunohistochemistry; subsequently, MMR assessment was evaluated as either proficient or as deficient by pathologists. The clinicopathological features and MMR status were compared using the Chi-square test. Univariate and multivariate analyses were conducted to identify prognostic factors.

RESULTS

Among the 102 CCA patients, dMMR was detected in 22.5%. Survival analysis revealed that dMMR patients had better survival than pMMR (HR = 0.50, p = 0.008). In multivariate analysis, dMMR was an independent factor for a good prognosis in CCA patients (HR = 0.58, p = 0.041), especially at an early stage (HR = 0.18, p = 0.027). Moreover, subgroup analysis showed dMMR patients who received adjuvant chemotherapy had better survival than surgery alone (HR = 0.28, p = 0.012).

CONCLUSION

This study showed a high prevalence of dMMR in cholangiocarcinoma with dMMR being the independent prognostic factor for good survival, especially in early-stage CCA and for patients who received adjuvant chemotherapy. dMMR should be the marker for selecting patients to receive a specific adjuvant treatment after resection for CCA.

Prognostic Significance of ARID1A Expression Patterns Varies with Molecular Subtype in Advanced Gastric Cancer

Background/Aims

AT-rich interactive domain 1A (ARID1A) is frequently mutated in gastric cancer (GC), especially Epstein-Barr virus (EBV)-associated and microsatellite instability high GC. The loss of ARID1A expression has been reported as a poor prognostic marker in GC. However, the relationships between ARID1A alteration and EBV-associated and microsatellite instability high GC, which are known to have a favorable prognosis, has hampered proper evaluation of the prognostic significance of ARID1A expression in GC. We aimed to analyze the true prognostic significance of ARID1A expression by correcting confounding variables.

Methods

We evaluated the ARID1A expression in a large series (n=1,032) of advanced GC and analyzed the relationships between expression pattern and variable parameters, including clinicopathologic factors, key molecular features such as EBV-positivity, mismatch repair protein deficiency, and expression of p53 and several receptor tyrosine kinases including human epidermal growth factor receptor 2, epidermal growth factor receptor, and mesenchymal-epithelial transition factor. Survival analysis of the molecular subtypes was done according to the ARID1A expression patterns.

Results

Loss of ARID1A expression was found in 52.5% (53/101) of mutL homolog 1 (MLH1)-deficient and 35.8% (24/67) of EBV-positive GCs, compared with only 9.6% (82/864) of the MLH1-proficient and EBV-negative group (p<0.001). The loss of ARID1A expression was associated only with MLH1 deficiency and EBV positivity. On survival analysis, the loss of ARID1A expression was associated with worse prognosis only in MLH1-proficient and EBV-negative GC. Multivariate analysis revealed that both loss of ARID1A and decreased ARID1A expression were independent worse prognostic factors in patients with advanced GC.

Conclusions

Only in MLH1-proficient and EBV-negative GC, the loss of ARID1A expression is related to poorer prognosis.

Assessment of the reliability of MSI status and dMMR proteins deficiency screening on endoscopic biopsy material in esophagus and gastric adenocarcinoma

BACKGROUND

Microsatellite instability (MSI) is a negative predictive factor for neoadjuvant chemotherapy in resectable oesogastric adenocarcinoma and a crucial determinant for immunotherapy. We aimed to evaluate reliability of dMMR/MSI status screening performed on preoperative endoscopic biopsies.

METHODS

Paired pathological samples from biopsies and surgical specimen of oesogastric adenocarcinoma were retrospectively collected between 2009 and 2019. We compared dMMR status obtained by immunohistochemistry (IHC) and MSI status by PCR. dMMR/MSI status on surgical specimen was considered as reference.

RESULTS

PCR and IHC were conclusive on biopsies respectively for 53 (96.4%) and 47 (85.5%) of the 55 patients enrolled. IHC was not contributive for 1 surgical specimen. A third reading of IHC was carried out for 3 biopsies. MSI status was observed in 7 (12.5%) surgical specimens. When analyses were contributive, sensitivity and specificity of biopsies for dMMR/MSI were respectively 85% and 98% for PCR vs. 86% and 98% for IHC. Concordance rate between biopsies and surgical specimen was 96.2% for PCR and 97.8% for IHC.

CONCLUSIONS

Endoscopic biopsies are a suitable source of tissue for dMMR/MSI status determination in oesogastric adenocarcinoma which should be routinely performed at diagnosis to better adapt neoadjuvant treatment.

MINIABSTRACT

By comparison of dMMR phenotype obtained by immunohistochemistry and MSI status by PCR between match-paired samples of oesogastric cancer's endoscopic biopsies and surgical specimen, we observed that biopsies are a suitable source of tissue for dMMR/MSI status determination.

Clinical molecular subtyping reveals intrinsic mesenchymal reprogramming in gastric cancer cells

The mesenchymal cancer phenotype is known to be clinically related to treatment resistance and a poor prognosis. We identified gene signature-based molecular subtypes of gastric cancer (GC, n = 547) based on transcriptome data and validated their prognostic and predictive utility in multiple external cohorts. We subsequently examined their associations with tumor microenvironment (TME) features by employing cellular deconvolution methods and sequencing isolated GC populations. We further performed spatial transcriptomics analysis and immunohistochemistry, demonstrating the presence of GC cells in a partial epithelial-mesenchymal transition state. We performed network and pharmacogenomic database analyses to identify TGF-β signaling as a driver pathway and, thus, a therapeutic target. We further validated its expression in tumor cells in preclinical models and a single-cell dataset. Finally, we demonstrated that inhibition of TGF-β signaling negated mesenchymal/stem-like behavior and therapy resistance in GC cell lines and mouse xenograft models. In summary, we show that the mesenchymal GC phenotype could be driven by epithelial cancer cell-intrinsic TGF-β signaling and propose therapeutic strategies based on targeting the tumor-intrinsic mesenchymal reprogramming of medically intractable GC.

Impact of mismatch repair deficiency on tumour regression grade after neoadjuvant chemotherapy in localized gastroesophageal adenocarcinoma

BACKGROUND

The use of neoadjuvant chemotherapy (NAC) in patients with mismatch repair (MMR) deficient (dMMR) localized gastric and oeso-gastric junction (OGJ) adenocarcinoma is subject of debate. Histological response assessment might help to better evaluate the impact of dMMR on response to NAC.

METHODS

Patients with localized gastric/OGJ adenocarcinoma resected after NAC were retrospectively identified. MMR protein expression status was assessed by immunohistochemistry. The primary objective was the frequency of histological responders to NAC defined by tumour regression grade (TRG) using Mandard's (TRG1-2) and Becker's (TRG1) classifications, according to the MMR status.

RESULTS

In total, 247 patients with 43 dMMR and 204 pMMR gastric/OGJ adenocarcinoma were identified. Among dMMR tumours, 18 (42%) arose from the OGJ. Histological response (Becker TRG1-2) was observed for 28% and 35% of dMMR and pMMR tumours, respectively (p = 0.35). Similar results were observed with Mandard classification. With a median follow-up of 37.5 months, median disease-free and overall survival were not reached for the dMMR group.

CONCLUSION

Histological response after NAC in patients with localized dMMR gastric/OGJ adenocarcinoma is not statistically different to those with pMMR tumours. This study provides additional data for the discussion about avoiding NAC in patients with dMMR gastric/OGJ adenocarcinomas.

Comprehensive Study of Microsatellite Instability Testing and Its Comparison With Immunohistochemistry in Gastric Cancers

PURPOSE

In this study, polymerase chain reaction (PCR)-based microsatellite instability (MSI) testing was comprehensively analyzed and compared with immunohistochemistry (IHC) for mismatch repair (MMR) protein expression in patients with gastric cancer (GC).

MATERIALS AND METHODS

In 5,676 GC cases, PCR-based MSI testing using five microsatellites (BAT-26, BAT-25, D5S346, D2S123, and D17S250) and IHC for MLH1 were performed. Re-evaluation of MSI testing/MLH1 IHC and additional IHC for MSH2, MSH6, and PMS2 were performed in discordant/indeterminate cases.

RESULTS

Of the 5,676 cases, microsatellite stable (MSS)/MSI-low and intact MLH1 were observed in 5,082 cases (89.5%), whereas MSI-high (MSI-H) and loss of MLH1 expression were observed in 502 cases (8.8%). We re-evaluated the remaining 92 cases (1.6%) with a discordant/indeterminate status. Re-evaluation showed 1) 37 concordant cases (0.7%) (18 and 19 cases of MSI-H/MMR-deficient (dMMR) and MSS/MMR-proficient (pMMR), respectively), 2) 6 discordant cases (0.1%) (3 cases each of MSI-H/pMMR and MSS/dMMR), 3) 14 MSI indeterminate cases (0.2%) (1 case of dMMR and 13 cases of pMMR), and 4) 35 IHC indeterminate cases (0.6%) (22 and 13 cases of MSI-H and MSS, respectively). Finally, MSI-H or dMMR was observed in 549 cases (9.7%), of which 47 (0.8%) were additionally confirmed as MSI-H or dMMR by re-evaluation. Sensitivity was 99.3% for MSI testing and 95.4% for MMR IHC.

CONCLUSIONS

Considering the low incidence of MSI-H or dMMR, discordant/indeterminate results were occasionally identified in GCs, in which case complementary testing is required. These findings could help improve the accuracy of MSI/MMR testing in daily practice.

Mismatch Repair and Microsatellite Instability Testing for Immune Checkpoint Inhibitor Therapy: Guideline From the College of American Pathologists in Collaboration With the Association for Molecular Pathology and Fight Colorectal Cancer

CONTEXT.—

The US Food and Drug Administration (FDA) approved immune checkpoint inhibitor therapy for patients with advanced solid tumors that have DNA mismatch repair defects or high levels of microsatellite instability; however, the FDA provided no guidance on which specific clinical assays should be used to determine mismatch repair status.

OBJECTIVE.—

To develop an evidence-based guideline to identify the optimal clinical laboratory test to identify defects in DNA mismatch repair in patients with solid tumor malignancies who are being considered for immune checkpoint inhibitor therapy.

DESIGN.—

The College of American Pathologists convened an expert panel to perform a systematic review of the literature and develop recommendations. Using the National Academy of Medicine-endorsed Grading of Recommendations Assessment, Development and Evaluation approach, the recommendations were derived from available evidence, strength of that evidence, open comment feedback, and expert panel consensus. Mismatch repair immunohistochemistry, microsatellite instability derived from both polymerase chain reaction and next-generation sequencing, and tumor mutation burden derived from large panel next-generation sequencing were within scope.

RESULTS.—

Six recommendations and 3 good practice statements were developed. More evidence and evidence of higher quality were identified for colorectal cancer and other cancers of the gastrointestinal (GI) tract than for cancers arising outside the GI tract.

CONCLUSIONS.—

An optimal assay depends on cancer type. For most cancer types outside of the GI tract and the endometrium, there was insufficient published evidence to recommend a specific clinical assay. Absent published evidence, immunohistochemistry is an acceptable approach readily available in most clinical laboratories.

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 not been 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.

Molecular Pathology of Gastric Cancer

Gastric cancer (GC) is one of the most common lethal malignant neoplasms worldwide, with limited treatment options for both locally advanced and/or metastatic conditions, resulting in a dismal prognosis. Although the widely used morphological classifications may be helpful for endoscopic or surgical treatment choices, they are still insufficient to guide precise and/or personalized therapy for individual patients. Recent advances in genomic technology and high-throughput analysis may improve the understanding of molecular pathways associated with GC pathogenesis and aid in the classification of GC at the molecular level. Advances in next-generation sequencing have enabled the identification of several genetic alterations through single experiments. Thus, understanding the driver alterations involved in gastric carcinogenesis has become increasingly important because it can aid in the discovery of potential biomarkers and therapeutic targets. In this article, we review the molecular classifications of GC, focusing on The Cancer Genome Atlas (TCGA) classification. We further describe the currently available biomarker-targeted therapies and potential biomarker-guided therapies. This review will help clinicians by providing an inclusive understanding of the molecular pathology of GC and may assist in selecting the best treatment approaches for patients with GC.

Clinical Utility of Next-generation Sequencing in Real-world Cases: A Single-institution Study of Nine Cases

BACKGROUND/AIM

Targeted next-generation sequencing (NGS) is a well-established technique to detect pathogenic alterations in tumors. Indeed, it is the cornerstone of targeted therapy in precision medicine. We investigated the clinical utility of next-generation sequencing in real-world cases.

PATIENTS AND METHODS

We retrospectively selected six representative cancer cases, wherein targeted NGS played a pivotal role in the diagnosis and treatment of patients. Additionally, we analyzed three cases with rare, unusual pathogenic alterations.

RESULTS

Our NGS analysis revealed that four patients had TPR-ROS1, EGFR-RAD51, and NCOA4-RET fusions and MET exon 14 skipping mutation, respectively, which can be treated with targeted therapy. Furthermore, we used NGS as a diagnostic tool to confirm the origin of unknown primary malignant tumors in two cases. Interestingly, NGS also helped us identify the following cases: patients exhibiting BRCA1 and TP53 mutations that exhibited histological and immunohistochemical characteristics consistent with endometrioid carcinoma, patients with high-grade serous carcinoma not possessing a TP53 mutation, and patients with small cell lung cancer with a ERBB2 mutation and displaying no loss of RB1.

CONCLUSION

We recommend targeted NGS for the diagnoses and targeted therapy of cancer patients.

Deep Learning based on hematoxylin-eosin staining outperforms immunohistochemistry in predicting molecular subtypes of gastric adenocarcinoma

In gastric cancer (GC), there are four molecular subclasses that indicate whether patients respond to chemotherapy or immunotherapy, according to the TCGA. In clinical practice, however, not every patient undergoes molecular testing. Many laboratories have used well-implemented in situ techniques (IHC and EBER-ISH) to determine the subclasses in their cohorts. Although multiple stains are used, we show that a staining approach is unable to correctly discriminate all subclasses. As an alternative, we trained an ensemble convolutional neuronal network using bagging that can predict the molecular subclass directly from hematoxylin-eosin histology. We also identified patients with predicted intra-tumoral heterogeneity or with features from multiple subclasses, which challenges the postulated TCGA-based decision tree for GC subtyping. In the future, Deep Learning may enable targeted testing for molecular subtypes and targeted therapy for a broader group of GC patients. This article is protected by copyright. All rights reserved.

Gastric cancer molecular classification based on immunohistochemistry and in situ hybridization: Analysis in western patients after curative-intent surgery

BACKGROUND

Gastric cancer (GC) is a highly heterogeneous disease, and the identification of molecular subtyping of gastric adenocarcinoma emerged as a promising option to define therapeutic strategies and prognostic subgroups. However, the costs and technical complexity of molecular methodologies remains an obstacle to its adoption, and their clinical significance by other approaches needs further evidence.

AIM

To evaluate the clinicopathological characteristics and long-term survival of GC based on the subgroups of molecular classification by immunohistochemistry (IHC) and in situ hybridization (ISH).

METHODS

We retrospectively evaluated all patients who underwent D2-gastrectomy between 2009 and 2016 in a Western cohort of GC patients treated with curative intent. Microsatellite instability (MSI) status, E-cadherin, and p53 expression were analyzed by IHC, and Epstein-Barr virus (EBV) by ISH. Tissue microarrays were constructed for analysis. Clinicopathological characteristics and survival of GC were evaluated according to subtypes defined by The Cancer Genome Atlas (TCGA) Research Network Group and Asian Cancer Research Group (ACRG) classification systems.

RESULTS

A total of 287 GC patients were included. Based on IHC and ISH analysis, five profiles were defined as follows: E-cadherin aberrant (9.1%), MSI (20.9%), p53 aberrant (36.6%), EBV positivity (10.5%), and p53 normal (31%), which corresponded to tumors that showed no alteration in another profile. A flowchart according to the TCGA and ACRG classifications were used to define the subtypes, where clinical and pathological characteristics associated with GC subtypes were evidenced. Proximal location (P < 0.001), total gastrectomy (P = 0.001), and intense inflammatory infiltrate (P < 0.001) were characteristics related to EBV subtype. MSI subtype was predominantly associated with advanced age (P = 0.017) and the presence of comorbidities (P = 0.011). While Laurén diffuse type (P < 0.001) and advanced stage (P = 0.029) were related to genomically stable (GS) subtype. GS tumors and microsatellite stable/epithelial to mesenchymal transition phenotype subtype had worse disease-free survival (DFS) and overall survival (OS) than other subtypes. Conversely, MSI subtype of GC had better survival in both classifications. Type of gastrectomy, pT and the TCGA subtypes were independent factors associated to DFS and OS.

CONCLUSION

The IHC/ISH analysis was able to distinguish immunophenotypic groups of GC with distinct characteristics and prognosis, resembling the subtypes of the molecular classifications. Accordingly, this method of classification may represent a viable option for use in a clinical setting.

CDX-1/CDX-2 Expression Is a Favorable Prognostic Factor in Epstein-Barr Virus-Negative, Mismatch Repair-Proficient Advanced Gastric Cancers

Background/Aims

Caudal type homeobox (CDX)-1 and -2 are reportedly involved in the development and progression of gastric cancer (GC). Although there are several reports on the prognostic significance of CDX-2 expression in GC, it remains controversial. In this study, we sought to validate the prognostic value of CDX-1 and -2 expression according to the histologic and molecular subtypes of GC.

Methods

In total, 1,158 cases of advanced GC were investigated using immunohistochemical staining and tissue microarrays for CDX-1 and -2 expression, and survival analysis was performed according to different histological and molecular subtypes.

Results

Of the 915 GCs with CDX-1 expression, 163 (17.8%) were Epstein-Barr virus (EBV)-positive or mismatch repair deficient (MMR-d), and the remaining 752 (82.2%) were EBV-negative or MMR-proficient (MMR-p). Of the 1,008 GCs with CDX-2 expression, 177 (17.5%) were EBV-positive or MMR-d, and the remaining 831 (82.5%) were EBV-negative or MMR-p. In the EBV-positive and MMR-d groups, CDX expression had no relationship with patient outcomes. In the EBV-negative and MMR-p groups, 404 (53.7%) and 523 (62.9%) samples were positive for CDX-1 and CDX-2 expression, respectively. Survival analysis demonstrated that CDX-1 and CDX-2 expression in all patients was correlated with favorable outcomes in terms of overall survival (multivariate analysis; p=0.018 and p=0.028, respectively). In the subgroup analysis, CDX-1 expression and CDX-2 expression were associated with favorable outcomes in EBV-negative and MMR-p intestinal (p=0.015 and p=0.010), and mixed and diffuse-type (p=0.019 and p=0.042) GCs, respectively.

Conclusions

The expression of CDX-1 and CDX-2 is a favorable prognostic factor in EBV-negative, MMR-p advanced GC. (Gut Liver 2021;15-704)

Unusual immunohistochemical “null” pattern of four mismatch repair proteins in gastric cancer: A case report

BACKGROUND

Immunohistochemical (IHC) staining for mismatch repair (MMR) proteins is useful for gastric cancer treatment and prognosis. Different IHC staining patterns reflect the complex biological phenomena underlying MMR deficiency. We herein report a rare IHC staining pattern of four MMR-related proteins in gastric cancer.

CASE SUMMARY

A “null” IHC staining pattern of four MMR-related proteins, including MLH1, PMS2, MSH2, and MSH6, in a 67-year-old male patient with gastric cancer pT3N3aM0 revealed promoter hypermethylation of MLH1. Next-generation sequencing showed that these four genes exhibited changes. One of these was the somatic mutation of the missing copy number in exon 14 of MSH2. Mutation analysis using peripheral blood showed no germline mutations in these four genes. The patient had no history of personal or family tumor history. We classified this case as sporadic. The patient returned to normal after operation, and there were no signs of tumor metastasis and recurrence. After six cycles of adjuvant chemotherapy, the patient was discharged in a stable condition. The patient had a mild reaction to chemotherapy and a good prognosis. At present, 16 mo after the operation, the patient's condition is stable.

CONCLUSION

Abnormal MMR protein expression, helpful for individualized follow-up care, helped identify a sporadic case lacking familial clinical management implications.

Microsatellite instability and Epstein-Barr virus combined with PD-L1 could serve as a potential strategy for predicting the prognosis and efficacy of postoperative chemotherapy in gastric cancer

Background

Microsatellite instability (MSI) and Epstein-Barr virus (EBV)-positive molecular subtypes exhibit complex immune responses in gastric cancer (GC), and PD-L1 has emerged as a prognostic biomarker associated with the cancer immune microenvironment. This study aimed to determine the prognostic value of molecular subtypes and whether the addition of PD-L1 would accurately predict the prognosis and guide postoperative chemotherapy for GC patients.

Methods

We performed molecular subtyping of tissue microarray slides from 226 GC patients who were treated with radical gastrectomy. The MSI status and PD-L1 expression were evaluated through immunohistochemistry (IHC) and EBV status through situ hybridization. Multiplex polymerase chain reaction (PCR) was also performed on 50 cases to validate the accuracy of IHC in defining MSI status. Differences in overall survival (OS) were assessed using the Kaplan-Meier method, log-rank test and Cox proportional hazards regression model.

Results

Among the 226 GC patients, 52 (23.2%) patients were classified as the MSI subtype, 11 (4.9%) were EBV⁺ subtype, and 161 (71.9%) were MSS (Microsatellite stable) /EBV subtype according to TCGA analysis. Two patients were both positive for MSI and EBV infection. EBV⁺ cases showed higher PD-L1 positivity than MSI cases and MSS/EBV cases (81.8% vs. 50.0% vs. 35.4%, P = 0.003). Compared with the non-MSS/EBV (MSI or EBV⁺ cases) subgroup, GC patients with MSS/EBV were associated with the worst outcomes (HR = 1.610, 95% CI [1.0462.479], P = 0.031). MSS/EBV GCs alone could benefit from postoperative chemotherapy (HR = 0.452, 95% CI [0.2990.682], P<0.001), and PD-L1-positive expression could also predict a better prognosis (HR = 0.612, 95% CI [0.3890.962], P = 0.033) in this subgroup. Considering both chemotherapy efficacy and PD-L1 expression in the MSS/EBV subgroup, chemotherapy could improve the prognosis for PD-L1-negative MSS/EBV GCs (HR = 0.357, 95% CI [0.2170.587], P <0.001) but not PD-L1-positive MSS/EBV GCs.

Conclusions

Molecular subtyping combined with PD-L1 expression could serve as a potential strategy to better predict prognosis and guide postoperative chemotherapy of GC patients.

Detection of Microsatellite Instability: State of the Art and Future Applications in Circulating Tumour DNA (ctDNA)

Simple Summary

Microsatellite instability (MSI) is a molecular fingerprint for defects in the mismatch repair system (dMMR) and is associated with higher risks of cancers. MSI/dMMR tumours are characterized by the accumulation of mutations throughout the genome, and particularly in microsatellite (MS) DNA repeat sequences. MSI stands as a major biomarker for familial cancer risk assessment, cancer prognosis, and therapeutic choices. Standard-of-care classification of MSI/dMMR tumours is most frequently achieved using immunohistochemistry or PCR-based assay directed against a set of five MS regions. However, novel molecular methods based on tumour tissue or plasma samples have been developed and could enter in the future trends of MSI testing. Here, we provide insights into these emerging approaches and discuss their advantages and limitations.

Abstract

Microsatellite instability (MSI) is a molecular scar resulting from a defective mismatch repair system (dMMR) and associated with various malignancies. MSI tumours are characterized by the accumulation of mutations throughout the genome and particularly clustered in highly repetitive microsatellite (MS) regions. MSI/dMMR status is routinely assessed in solid tumours for the initial screening of Lynch syndrome, the evaluation of cancer prognosis, and treatment decision-making. Currently, pentaplex PCR-based methods and MMR immunohistochemistry on tumour tissue samples are the standard diagnostic methods for MSI/dMMR. Other tissue methods such as next-generation sequencing or real-time PCR-based systems have emerged and represent viable alternatives to standard MSI testing in specific settings. The evolution of the standard molecular techniques has offered the opportunity to extend MSI determination to liquid biopsy based on the analysis of cell-free DNA (cfDNA) in plasma. This review aims at synthetizing the standard and emerging techniques used on tumour tissue samples for MSI/dMMR determination. We also provide insights into the MSI molecular techniques compatible with liquid biopsy and the potential clinical consequences for patients with solid cancers.

Immunohistochemical Expression Pattern of MLH1, MSH2, MSH6, and PMS2 in Tumor Specimen of Iranian Gastric Carcinoma Patients

BACKGROUND

Gastric cancer is the third leading cause of cancer-related death. Determining molecular and histopathologic tumor features, which may contribute to the development or progression of gastric cancer, can improve the prognosis. Expression patterns of DNA repair proteins such as MLH1, MSH2, MSH6, and PMS2 that are associated with microsatellite instability (MSI) are some of the markers that are useful in predicting the prognosis of gastric cancer.

PURPOSE

The purpose was to determine the immunohistochemical expression pattern of MLH1, MSH2, MSH6, and PMS2 in tumor specimens of Iranian gastric carcinoma patients.

METHODS

In this prospective cohort, 186 consecutive patients with gastric cancer, attending Taleghani Hospital, were enrolled. The immunohistochemical expression patterns of MLH1, MSH2, MSH6, and PMS2 in tumor specimens among them were determined.

RESULTS

The results of this study demonstrated that 91.4% of our gastric cancer patients were negative for MSI, and 8.6% of them were MSI positive. The positive MSI was seen in 5.9% and 15.7% of male and female subjects, respectively, with a significant difference (P = 0.043). The other variables were not related to MSI results (P > 0.05).

CONCLUSION

According to the obtained results, the expression of MLH1, MSH2, MSH6, and PMS2 in tumor specimens is positive in 8.6% of the total Iranian gastric cancer sample size, which is mainly positive in female subjects. However, it is not related to the location and stage of the tumor.

Comprehensive Immuno-Molecular Profiles for Liposarcoma: Roles of Programmed Death Ligand 1, Microsatellite Instability, and PIK3CA

BACKGROUND

Developing personalized strategies for cancer has shown good efficacies.

METHODS

We assessed the molecular targets programmed death ligand 1 (PD-L1), microsatellite instability (MSI), and PIK3CA. Seventy-four patients with liposarcomas who underwent curative resection were assessed for PD-L1 expression in the tumor and tumor-infiltrating lymphocytes (TILs), mismatch repair proteins (MLH1, PMS2, MSH2, and MSH6) by immunohistochemistry, MSI using polymerase chain reaction, and PIK3CA mutation/amplification using pyrosequencing and fluorescence in situ hybridization.

RESULTS

Seventeen (23%) cases were TIL+ (≥1 + expression) and associated with longer 5-year overall survival than those with TIL- tumors (84.4 vs. 60.8%, p = 0.007). Six (35.3%) PD-L1+ tumors were detected only in TIL+ cases, with none detected in tumor cells. Two well-differentiated liposarcomas showed MSI, one low and one high with concurrent loss of MLH1, MSH6, and PMS2. PIK3CA mutation was detected in 7 (9.5%) [exon 9 (n = 4) and exon 20 (n = 3)] and only 1 Q546K mutation was a PD-L1+ tumor. PIK3CA copy number gain was detected in 18 (24.4%) and was associated with TIL+ tumors (p = 0.045).

CONCLUSIONS

Our comprehensive immuno-molecular panel suggests that liposarcoma should be categorized based on the molecular genomic subtype for precision medicine.

Prognostic perspectives of PD-L1 combined with tumor-infiltrating lymphocytes, Epstein-Barr virus, and microsatellite instability in gastric carcinomas

Background

The prognostic potential of PD-L1 is currently unclear in gastric carcinomas, although the immune checkpoint PD-1/PD-L1 inhibitors have produced promising results in clinical trials.

Methods

We explored the prognostic implications of programmed death ligand 1 (PD-L1) in 514 consecutive surgically-resected gastric carcinomas. Overall survival and recurrence-free survival were evaluated. Immunohistochemistry for PD-L1, CD8, FOXP3, and PD-1, and molecular grouping by in situ hybridization for Epstein-Barr virus (EBV)-encoded small RNAs and multiplex PCR for microsatellite instability (MSI) markers were performed. Additionally, to explore the function inherent to PD-L1, PD-L1-specific siRNA transfection, cell proliferation, invasion, migration and apoptosis assays were conducted in five gastric carcinoma cell lines.

Results

PD-L1(+) tumor and immune cells were observed in 101 (20%) and 244 patients (47%), respectively. “Tumoral PD-L1(+)/immune cell PD-L1(-)/CD8^+/low tumor-infiltrating lymphocytes (TILs),” and more advanced-stage tumors were associated with unfavorable clinical outcomes in the entire cohort through multivariate analysis. Furthermore, tumoral PD-L1(+)/FOXP3^+/low TILs were associated with worse clinical outcomes in EBV-positive and MSI-high carcinomas. Tumoral PD-L1(+) alone was an adverse prognostic factor in EBV-positive carcinomas, but not in MSI-high carcinomas, whereas PD-L1(+) immune cells or FOXP3^+/high TILs alone were correlated with a favorable prognosis. PD-L1 knockdown in gastric carcinoma cells suppressed cell proliferation, invasion and migration, and increased apoptosis, which were all statistically significant in two EBV(+) cell lines, but not all in three EBV(−) cell lines.

Conclusions

The prognostic impact of PD-L1 may depend on the tumor microenvironment, and statuses of EBV and MSI, although PD-L1 innately promotes cancer cell survival in cell-based assays. The combination of “tumoral PD-L1/immune cell PD-L1/CD8⁺ TILs” may serve as an independent prognostic factor. Tumoral PD-L1(+)/immune cell PD-L1(−)/CD8^+/low TILs showing a worse prognosis may be beneficial for combinatorial therapies of anti-PD-L1/PD-1 and anti-cytotoxic T-lymphocyte associated antigen 4 (CTLA4) that would promote effector T cells, thus attack the tumor.

[Hereditary gastric cancer: Challenges for the pathologist in 2020]

Gastric cancer is the third most common cancer worldwide. The majority of gastric cancers are sporadic but familial clustering is seen in more than 10% of cases. This manuscript is divided into two parts. The first part is dedicated to the non-syndromic hereditary gastric cancer, particularly the hereditary diffuse gastric cancer (HDGC) and other gastric polyposes including the recently described GAPPS (Gastric adenocarcinoma and proximal polyposis of the stomach). The second part concerns the syndromic gastric cancer, namely the HNPCC syndrome (Hereditary Non Polyposis Colorectal Cancer) occurring as part of a genetic predisposition syndrome to cancer. Recent advances in oncogenetics and next generation sequencing technology have enabled the identification of new entities. This enhancement in knowledge regarding inherited syndromes predisposing to gastric cancer has consequently improved the management of patients and their families. In this context, pathologists play a major role in identifying particular morphologic entities prompting genetic investigation. The aim of this manuscript is to provide an update on the current knowledge about hereditary gastric cancer.

[Localized MSI/dMMR gastric cancer patients, perioperative immunotherapy instead of chemotherapy: The GERCOR NEONIPIGA phase II study is opened to recruitment]

INTRODUCTION

Perioperative chemotherapy is the standard strategy for localized gastric cancers. Nevertheless, this strategy seems to be inefficient, if not deleterious, for patients with tumors harboring microsatellite instability (MSI) and/or mismatch repair deficiency (dMMR), a tumor phenotype predictive for the efficacy of immune checkpoint inhibitors (ICKi).

AIM

The GERCOR NEONIPIGA single-arm phase II study (NCT04006262; EUDRACT 2018-004712-22) aims at evaluating the efficacy of a peri-operative strategy with nivolumab and ipilimumab in neoadjuvant setting, then nivolumab alone after surgery for patients with resectable MSI/dMMR gastric cancer.

MATERIAL AND METHODS

Main inclusion criteria are: gastric and oesogastric junction adenocarcinoma (GOA), T2-T4, all N stage and M0, MSI/dMMR. Patients will be treated with nivolumab 240mg Q2W, 6 infusions, and ipilimumab 1mg/kg Q6W, 2 infusions in neoadjuvant setting. Following surgery, patients with TRG 1-2-3 (Mandard tumor regression grade), acceptable tolerance of neoadjuvant treatment and postoperative ECOG performance status 0-1, will be treated with adjuvant nivolumab 480mg Q4W, 9 infusions.

RESULTS

The primary endpoint is pathological complete response rate (pCR-R). Based on a Fleming design, with α=5% and β=20%, 27 patients have to be evaluated (H0=5%; H1=20%). Secondary endpoints include disease-free survival, overall survival and safety.

CONCLUSION

This study is planned to include 32 patients to evaluate the pCR-R with the combination of nivolumab and ipilimumab in neoadjuvant setting for MSI/dMMR localized GOA. The MSI/MMR status should be systematically assessed on diagnostic biopsies of all GOA. If it meets its primary endpoint, the GERCOR NEONIPIGA study might mark a turning point in the management of localized MSI/dMMR GOA patients.

Nivolumab in Heavily Pretreated Metastatic Gastric Cancer Patients: Real-Life Data from a Western Population

PURPOSE

ATTRACTION-2 trial assessed the role of Nivolumab as a new standard treatment for Asian patients with pretreated metastatic gastric cancer (mGC). The aim of this analysis was to evaluate the safety and efficacy of Nivolumab in a real-life Western population, considering the lack of evidence to date.

PATIENTS AND METHODS

Patients progressed after ≥2 chemotherapy regimens and able to receive Nivolumab (3 mg/kg q14) were eligible for the analysis.

RESULTS

16 patients received Nivolumab as third (81.3%) or fourth line (18.7%) from September 2017 to July 2019. The safety was in line with the literature and only one patient discontinued treatment due to persistent hematological toxicity. Overall response rate and disease control rate were 18.7% and 31.2%, respectively. Median duration of response was 5 months. With a median follow-up of 21 months, median OS was 6 months (7, 21 and 22 months in the responders) and median PFS 3 months. PD-L1 and microsatellite status were retrospectively collected in 12 patients. All the major responders were MSI, although no statistically significant difference in OS or PFS was observed according to molecular analysis.

CONCLUSION

Nivolumab is feasible and effective in Western patients with mGC. Further investigation is urgently needed also in non-Asians.

Microsatellite instability: a review of what the oncologist should know

The patients with high microsatellite instability (MSI-H)/mismatch repair deficient (dMMR) tumors recently have been reported that can benefit from immunotherapy, and MSI can be used as a genetic instability of a tumor detection index. However, many studies have shown that there are many heterogeneous phenomena in patients with MSI tumors in terms of immunotherapy, prognosis and chemotherapy sensitivity. Here we mainly review the research results of MSI detection methods, the mechanisms of MSI occurrence and its relationship with related tumors, aiming to make a brief analysis of the current research status of MSI and provide comparable reference and guidance value for further research in this field.

Histo- and immunohistochemistry-based estimation of the TCGA and ACRG molecular subtypes for gastric carcinoma and their prognostic significance: A single-institution study

Gastric cancers comprise molecularly heterogeneous diseases; four molecular subtypes were identified in the cancer genome atlas (TCGA) study, with implications in patient management. In our efforts to devise a clinically feasible means of subtyping, we devised an algorithm based on histology and five stains available in most academic pathology laboratories. This algorithm was used to subtype our cohort of 107 gastric cancer patients from a single institution (St. Michael’s Hospital, Toronto, Canada), which was divided into 3 cases of EBV-positive, 23 of MSI, 27 of GS and 54 of CIN tumours. 87% of the tumours with diffuse histology were classified as GS subtype, which was notable for younger age. Examining for characteristic molecular features, aberrant p53 immunostaining was seen most frequently in the CIN subtype (43% in CIN vs. 6% in others), whereas ARID1A loss was rarely seen (6% vs. 35% in others). HER2 overexpression was seen exclusively in CIN tumours (17% of CIN tumours). PD-L1 positivity was seen predominantly in the EBV and MSI tumours. As with the TCGA study, no survival differences were seen between the subtypes. A similar strategy was employed to approximate the Asian Cancer Research Group (ACRG) molecular subtyping, with the addition of p53 IHC to the algorithm. We observed rates of ARID1A loss and HER2 overexpression that were comparable to the ACRG study. In summary, our algorithm allowed for clinically feasible means of subtyping gastric carcinoma that recapitulated the key molecular features reported in the large scale studies.

Tumor immune response and immunotherapy in gastric cancer

Remarkable developments in immuno-oncology have changed the landscape of gastric cancer (GC) treatment. Because immunotherapy intervenes with tumor immune response rather than directly targeting tumor cells, it is important to develop a greater understanding of tumor immunity. This review paper summarizes the tumor immune reaction and immune escape mechanisms while focusing on the role of T cells and their co-inhibitory signals, such as the immune checkpoint molecules programmed death-1 and programmed deathligand 1 (PD-L1). This paper also describes past clinical trials of immunotherapy for patients with GC and details their clinical implications. Strong predictive markers are essential to improve response to immunotherapy. Microsatellite instability, Epstein-Barr virus, PD-L1 expression, and tumor mutational burden are now regarded as potent predictive markers for immunotherapy in patients with GC. Novel immunotherapy and combination therapy targeting new immune checkpoint molecules such as lymphocyte-activation gene 3, T cell immunoglobulin, and mucin domain containing-3, and indoleamine 2,3-dioxygenase have been suggested, and trials are ongoing to evaluate their safety and efficacy. Immunotherapy is an important treatment option for patients with GC and has great potential for improving patient outcome, and further research in immuno-oncology should be carried out.

Prognostic value of mismatch repair deficiency in patients with advanced gastric cancer, treated by surgery and adjuvant 5-fluorouracil and leucovorin chemoradiotherapy

OBJECTIVE

The predictive value of mismatch repair protein deficiency (MMRD) for chemoradiotherapeutic outcome has rarely been reported in gastric cancer. This study investigated the clinical significance of MMRD as a prognostic factor for tumor recurrence, and as a predictor of response to adjuvant chemoradiotherapy in advanced gastric cancer patients.

METHODS

Between 1995 and 2008, tissue specimens of 881 patients who underwent radical gastrectomy for stage II and III gastric cancer were analyzed. MMRD was assessed using immunohistochemical stains for MLH1, PMS2, MSH2, and MSH6. Patients were divided into two groups according to adjuvant treatment: a 5-fluorouracil/leucovorin (FL) adjuvant chemoradiotherapy group and a surgery alone group. Disease-free survival (DFS) was compared between the two groups correlated to MMRD. Risk factors for tumor recurrence were analyzed using multivariate analysis.

RESULTS

Of the 881 gastric cancer patients, 88 (10.0%) exhibited MMRD and 398 (45.2%) patients received adjuvant FL chemoradiotherapy. The multivariate analysis revealed that MMRD was a good independent prognostic factor (hazard ratio, 0.572; 95% confidence interval, 0.370-0.883; P = 0.012). For stage III gastric cancer displaying mismatch repair protein proficiency (MMRP), adjuvant FL chemoradiotherapy after surgery resulted in better DFS than surgery alone (P = 0.001). Among the stage II gastric cancer patients, adjuvant FL chemoradiotherapy did not show survival benefit, regardless of MMRD.

CONCLUSION

MMRD is a good independent prognostic factor in advanced gastric cancer. Adjuvant FL chemoradiotherapy was beneficial in patients with stage III gastric cancer with MMRP but not in those with MMRD.

Assessing molecular subtypes of gastric cancer: microsatellite unstable and Epstein-Barr virus subtypes. Methods for detection and clinical and pathological implications

Background

The molecular classification of gastric cancer recognises two subtypes prone to immune checkpoint blockade: the microsatellite unstable and the Epstein-Barr virus (EBV)-related tumours. We aim to assess the concordance between immunohistochemistry and PCR for microsatellite status evaluation, and explore the value of microsatellite instability (MSI) and EBV as predictive survival factors.

Material and methods

We collected 246 consecutively diagnosed gastric cancer cases in all stages and evaluated the microsatellite status using immunohistochemistry for mismatched repair (MMR) proteins and PCR. EBV expression was studied through in situ hybridisation.

Results

Forty-five (18%) cases presented MSI and 13 (6%) were positive for EBV. MSI was associated with female sex, older age, distal location and distal non-diffuse type of the modified Lauren classification. EBV expression was most frequent in proximal location and proximal non-diffuse type. The sensitivity, specificity, positive predictive value and negative predictive value of immunohistochemistry for the microsatellite study were 91%, 98%, 91% and 98%, respectively. In the multivariate analysis, MSI was an independent predictor of favourable tumour-specific survival (TSS) in stages I–III (MSI: HR: 0.37, 95% CI 0.12 to 0.95, p=0.04).

Conclusions

The MSI status and the EBV expression should be incorporated in routine pathological report for two reasons. First, MSI defines a different pathological entity with a better outcome. Second, MSI and EBV may be useful biomarkers to identify patients who will respond to immune checkpoint blockade inhibitors. For this purpose, immunohistochemical study for MMR proteins and in situ hybridisation study for EBV evaluation are feasible and cost-effective methods.

Subtraction of Epstein-Barr virus and microsatellite instability genotypes from the Lauren histotypes: Combined molecular and histologic subtyping with clinicopathological and prognostic significance validated in a cohort of 1,248 cases

Limited studies investigated clinicopathological and prognostic significance of histologic and molecular subgroups of gastric cancer concurrently. We retrospectively enrolled 1,248 patients with gastric cancer who received radical gastrectomy with lymphadenectomy and classified these cases into the Epstein-Barr virus (EBV)-associated and microsatellite instability (MSI)-associated subtypes by EBV-encoded small RNA in situ hybridization and immunohistochemical stains for DNA mismatch repair proteins, respectively. The remaining cases were categorized as the Lauren intestinal and diffuse/mixed subtypes. The clinicopathological and prognostic significance of the subtypes was examined by statistical analysis. In total, 65 (5.2%), 116 (9.3%), 496 (39.7%), 431 (34.5%) and 140 (11.2%) cases were identified as EBV-associated, MSI-associated, intestinal, diffuse and mixed subtypes, respectively. The EBV-associated, MSI-associated, intestinal and diffuse/mixed subtypes exhibited distinctive clinicopathological characteristics, including differences in age, gender, stump cancer, gastric location, tumor size, TNM stage, margin involvement, lymphatic/perineural invasion, HER2 status and recurrence pattern. The log-rank test showed survival discrimination (p < 0.001), and the multivariate analysis identified EBV-associated and MSI-associated cases demonstrated better outcomes than the diffuse/mixed subtype (EBV, HR 0.464, 95% CI 0.296-0.727, p = 0.001; MSI, HR 0.590, 95% CI 0.407-0.856, p = 0.005). EBV-associated lymphoepithelioma-like carcinoma cases had the most favorable outcome (HR 0.138, 95% CI 0.033-0.565, p = 0.006). In different clinical groups, the subtypes exhibited survival discrepancies. The EBV-associated and diffuse/mixed cases exhibited more favorable response to chemotherapy. In conclusion, this combined classification, in parallel with the molecular subtypes specified in the Cancer Genome Atlas study, has implications for the clinical management of gastric cancer.

MSI/MMR-deficient tumor diagnosis: Which standard for screening and for diagnosis? Diagnostic modalities for the colon and other sites: Differences between tumors

Microsatellite instability (MSI), which is caused by deficiency of the DNA mismatch repair (MMR) system, is the molecular abnormality observed in tumors associated with Lynch syndrome. Lynch syndrome represents one of the most frequent conditions of cancer predisposition in human, thus requiring specific care and genetic counseling. Moreover, research has recently focused increasingly on MMR deficiency due to its positive predictive value for the efficacy of immune checkpoints inhibitors (ICKi) in metastatic tumors, regardless of their primary origin. MSI has also been demonstrated to constitute an independent prognostic factor in several tumor types, being also associated with alternative response to chemotherapy. These observations have led many professional medical organizations to recommend universal screening of all newly diagnosed colorectal cancers for dMMR/MSI status and increasing evidence support the evaluation of MSI in all human tumors regardless of the cancer tissue of origin. Currently, two standard reference methods, namely immunohistochemistry and polymerase chain reaction, are recommended for the detection of dMMR/MSI status. These methods are equally valid as the initial screening test for dMMR/MSI in colorectal cancer. To date, there is no recommendation for the detection of dMMR/MSI in other primary tumors. In this review, we will present a comprehensive overview of the methods used for evaluation of tumor dMMR/MSI status in colorectal cancer, as well as in other tumor sites. We will see that the evaluation of this status remains challenging in some clinical settings, with the need to improve the above methods in these specific contexts.

Clinicopathological features and prognostic value of mismatch repair protein deficiency in gastric cancer

The microsatellite instability (MSI) tumor is one of the four molecular subtypes in gastric cancer (GC). MSI tumors are sensitive to immune checkpoint blockade therapy. However the prevalence and characteristics of MSI in GCs remains unclear. We aimed to clarify relationships between MSI and clinicopathological features along with patients' survival rates. Data was collected from a cohort of 567 consecutive GC patients who received radical gastrectomy in Fudan University Shanghai Cancer Center. Expression of four DNA mismatch repair proteins (MMRPs)-MLH1, PSM2, MSH2, MSH6 was assessed using immunohistochemistry staining. Absence of any of the four MMRPs was defined as deficiency mismatch repair (dMMR). Tumors with preserved expression of all MMRPs were considered MMR-proficient (pMMR). Chi-squared test or Fisher's exact probability test was used to detect correlation between MMR status and clinicopathological parameters. Kaplan-Meier method and Log-rank test were used for survival analysis. Fifty-seven cases (57/567, 10.1%) were confirmed as dMMR. The dMMR status was in significant correlation with older age (p<0.001), female gender (p=0.016), distal tumor location in stomach (p=0.002), intestinal Lauren classification (p<0.001), less lymph node metastasis (p=0.040), and less nerve invasion (p=0.016). The dMMR tumors often exhibited unique nested, trabecular or solid growth pattern with an expanding margin and many infiltrating lymphocytes. Patients with dMMR phenotype had improved disease-free survival (p=0.024) and overall survival rates (p=0.025) compared to those with pMMR status. Cox regression analysis manifested dMMR status was an independent factor of better prognosis. In summary, GC with dMMR subtype had distinct clinicopathological features.

Comprehensive expression profiles of gastric cancer molecular subtypes by immunohistochemistry: implications for individualized therapy

Gastric cancer (GC) is a leading cause of death. We aim to establish a clinically relevant assay that encompasses recent molecular classifications and provides useful clinical information in a large cohort of GC patients. A consecutive series of 438 GC patients that underwent palliative chemotherapy between 2014 and 2015 were assessed using 10 GC panels: EBER in-situ hybridization, immunohistochemistry for mismatch repair (MMR) proteins (MLH1, PMS2, MSH2, and MSH6), receptor tyrosine kinases (RTKs; HER2, EGFR, and MET), PTEN, and p53 protein. With a median of one aberration, 3.3 % of samples analyzed were Epstein-Barr virus (EBV)-positive; 4.8%, MMR-deficient. RTKs were overexpressed in 218 patients; EGFR was most commonly overexpressed (39.9%), followed by HER2 (13.5%) and MET (12.1%). Furthermore, 2.5 % and 10.7 % of cases had simultaneous overexpression of three and two RTKs, respectively. p53 overexpression/null tumors were identified in 259 patients (59.1%), and PTEN loss was identified in 89 patients (20.3%). EBV-positivity was mutually exclusive with MMR-deficiency, predominantly identified in male patients, and these tumors were undifferentiated with proximal location. p53 mutant type was significantly found predominantly in the EBV-negative (60.6% vs 14.3%, P=0.001) and HER2-positive (78.0% vs 56.2%, P=0.002) groups. We described a molecular spectrum of distinct GC subtypes using clinically applicable assay. This assay will provide a convenient screening tool and facilitate the development of targeted agents in clinical trials.

Meta-analysis of microsatellite instability in relation to clinicopathological characteristics and overall survival in gastric cancer

BACKGROUND

Several associations between microsatellite instability (MSI) and other clinicopathological factors have been reported in gastric cancer, but the results have been ambiguous. This systematic review and meta-analysis investigated the relationship between MSI and overall survival and clinicopathological characteristics of patients with gastric cancer.

METHODS

A systematic literature search of the PubMed, Cochrane and Ovid databases until 31 January 2016 was performed in accordance with the PRISMA statement. The articles were screened independently according to PICO (population, intervention, comparator, outcome) eligibility criteria. All eligible articles were evaluated independently by two reviewers for risk of bias according to the Quality In Prognosis Study tool.

RESULTS

Overall, 48 studies with a total of 18 612 patients were included. MSI was found in 9·2 per cent of patients (1718 of 18 612), and was associated with female sex (odds ratio (OR) 1·57, 95 per cent c.i. 1·31 to 1·89; P < 0·001), older age (OR 1·58, 2·20 to 1·13; P < 0·001), intestinal Laurén histological type (OR 2·23, 1·94 to 2·57; P < 0·001), mid/lower gastric location (OR 0·38, 0·32 to 0·44; P < 0·001), lack of lymph node metastases (OR 0·70, 0·57 to 0·86, P < 0·001) and TNM stage I-II (OR 1·77, 1·47 to 2·13; P < 0·001). The pooled hazard ratio for overall survival of patients with MSI versus those with non-MSI gastric cancer from 21 studies was 0·69 (95 per cent c.i. 0·56 to 0·86; P < 0·001).

CONCLUSION

MSI in gastric cancer was associated with good overall survival, reflected in several favourable clinicopathological tumour characteristics.