The Role of Microsatellite Instability in Positive Margin Gastric Cancer Patients

Gastric Cancer: An Up-to-Date Review with New Insights into Early-Onset Gastric Cancer

Gastric cancer (GC) is the fifth most frequently diagnosed cancer and the fifth most common cause of cancer death in the world. Regarding the age at which the diagnosis was made, GC is divided into early-onset gastric cancer (EOGC-up to 45 years of age) and conventional GC (older than 45). EOGC constitutes approximately 10% of all GCs. Numerous reports indicate that EOGC is more aggressive than conventional GC and is often discovered at an advanced tumor stage, which has an impact on the five-year survival rate. The median survival rate for advanced-stage GC is very poor, amounting to less than 12 months. Risk factors for GC include family history, alcohol consumption, smoking, Helicobacter pylori, and Epstein-Barr virus infection. It has been shown that a proper diet and lifestyle can play a preventive role in GC. However, research indicates that risk factors for conventional GC are less correlated with EOGC. In addition, the unclear etiology of EOGC and the late diagnosis of this disease limit the possibilities of effective treatment. Genetic factors are considered a likely cause of EOGC, as young patients are less exposed to environmental carcinogens. Research characterizing GC in young patients is scarce. This comprehensive study presents all aspects: epidemiology, risk factors, new treatment strategies, and future directions.

Clinical and Genetic Characteristics of Early and Advanced Gastric Cancer

Gastric cancer (GC) persists as the fourth most prevalent cause of global cancer-related mortality, presenting a challenge due to the scarcity of available therapeutic strategies. Precision medicine is crucial not only in the treatment but also in the management of GC. We performed gene panel sequencing with Oncomine focus assay comprising 52 cancer-associated genes and MSI analysis in 100 case-matched gastric cancer cases. A comprehensive analysis of clinical and genetic characteristics was conducted on these genetic results and clinicopathological findings. Upon comparison of clinicopathological characteristics, significant differences between early gastric cancer (EGC) and advanced gastric cancer (AGC) were observed in tumor location (p = 0.003), Lauren classification (p = 0.015), T stage (p = 0.000), and N stage (p = 0.015). The six most frequently mutated genes were PIK3CA (29%, 10/35), ERBB2 (17%, 6/35), KRAS (14%, 5/35), ALK (6%, 2/35), ESR1 (6%, 2/35), and FGFR3 (6%, 2/35). Regarding genetic variation, there was a tendency for the N stage to be higher in GC patients with mutated genes (p = 0.014). The frequency of mutations in GC patients was statistically significantly higher in AGC (n = 24) compared to EGC (n = 11) (odds ratio, 2.792; 95% confidence interval, 1.113 to 7.007; p = 0.026). Six of the ten GC patients carrying mutated genes and exhibiting MSI were classified into intestinal-type and undifferentiated GC, with the location of the tumor being in the lower-third. Among these patients, five harbored mutated PIK3CA, while the remaining patient had a mutation in ALK. Conclusions: AGC patients more frequently exhibited alterations of PIK3CA, KRAS, and ERBB2 as somatic oncogenic drivers, and displayed a higher prevalence of cumulative genetic events, including increased rates of PIK3CA mutations, enhanced detection of immunotherapy biomarkers, and mutations of the ESR1 gene.

[Complicated gastric cancer and modern treatment approaches]

Among all patients with gastric cancer, 40% admit to the hospitals due to cancer-related complications. The most common complications of gastric cancer are bleeding (22-80%), malignant gastric outlet obstruction (26-60%), and perforation (less than 5%). The main treatment methods for gastric cancer complicated by bleeding are various forms of endoscopic hemostasis, transarterial embolization and external beam radiotherapy. Surgical treatment is possible in case of ineffective management. However, surgical algorithm is not standardized. Malignant gastric outlet stenosis requires decompression: endoscopic stenting, palliative gastroenterostomy. Surgical treatment is also possible (gastrectomy, proximal or distal resection of the stomach). The main problem for patients with complicated gastric cancer is the lack of standardized algorithms and abundance of potential surgical techniques. The aim of our review is to systematize available data on the treatment of complicated gastric cancer and to standardize existing methods.

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.

DNA Damage Repair and Current Therapeutic Approaches in Gastric Cancer: A Comprehensive Review

DNA in cells is frequently damaged by endogenous and exogenous agents. However, comprehensive mechanisms to combat and repair DNA damage have evolved to ensure genomic stability and integrity. Improper DNA damage repair may result in various diseases, including some types of tumors and autoimmune diseases. Therefore, DNA damage repair mechanisms have been proposed as novel antitumor drug targets. To date, numerous drugs targeting DNA damage mechanisms have been developed. For example, PARP inhibitors that elicit synthetic lethality are widely used in individualized cancer therapies. In this review, we describe the latent DNA damage repair mechanisms in gastric cancer, the types of DNA damage that can contribute to the development of gastric cancer, and new therapeutic approaches for gastric cancer that target DNA damage repair pathways.

Gastric medullary carcinoma: clinicopathological features and prognosis-a single-center study

BACKGROUND

Gastric medullary carcinoma (GMC) is a distinct histologic subtype of gastric adenocarcinoma, which prominently associated with Epstein-Barr virus infection. This study aimed to evaluate the clinicopathological features and prognosis of patients with medullary carcinoma in one center.

METHODS

Data regarding patients with gastric cancer were retrospectively analyzed at Marmara University between 2014 and 2019. Demographics, pathological features, and overall survival of patients with GMC were evaluated. The primary outcome of this study was to compare the pathological features of GMC to non-GMC (NGMC). The secondary outcome was comparing overall survival between the two groups.

RESULTS

A total of 412 patients were enrolled in the study. Of 412 patients, 19 (5%) were diagnosed with medullary cancer. Compared to NGMC, no significant differences were observed in patient age, gender, tumor macroscopic pattern, size, lymphovascular invasion, pathological stage, location and size of the tumors, and the number of metastatic lymph nodes in GMC. However, perineural invasion and Borrmann ulcerated type rates were significantly higher among NGMC. Whereas the microsatellite instability (MSI) rate was significantly higher in the GMC (64% and 11%, respectively, p < 0.001). Multivariate analysis showed that the MSI status was the solely significantly different feature between the two groups.

CONCLUSION

This study showed that GMC was associated with MSI, which could explain the better prognosis of medullary carcinomas.

MSI-WES: a simple approach for microsatellite instability testing using whole exome sequencing

Aim: To demonstrate that MSI-WES is an accurate testing method for microsatellite instability (MSI). Materials & methods: Microsatellite-based indels were counted in the variant call-formatted whole exome sequencing (WES) data of 441 gastric cancer cases using Unix-based algorithms, and the counts expressed as a fraction of the genome sequenced to obtain next-generation sequencing-based MSI indices. Results: The next-generation sequencing-based MSI indices showed a near-perfect concordance with PCR-based MSI status, and moderate to good correlations with the molecular targets of MSI index, MLH1 expression and MLH1 methylation status, at a level comparable to the strengths of correlation between PCR-based MSI status and molecular targets of MSI index/MLH1 expression and methylation. Conclusion: MSI-WES is a valid, adequate and sensitive approach for testing MSI in cancer.

Microsatellite instability in Gastric Cancer: Between lights and shadows

Gastric cancer (GC) represents an important contributor to the global burden of cancer, being one of the most common and deadly malignancies worldwide. According to TCGA and ACRG classifications, the microsatellite instable (MSI) group represents a significant subset of GCs and is currently in the limelight of many researches due to its favorable survival outcome in resectable stages compared to microsatellite stable tumors. MSI GCs hypermutated phenotype triggers immunosurveillance, making this molecular subgroup a promising candidate for immune checkpoint inhibitors treatment. Conversely, conflicting outcomes have been reported in chemotherapy settings. Due to the clinical relevance of these observations, in this review we report and discuss the molecular, pathological, prognostic, and predictive features of MSI gastric tumors.

Gastric Cancer: Epidemiology, Risk Factors, Classification, Genomic Characteristics and Treatment Strategies

Gastric cancer (GC) is one of the most common malignancies worldwide and it is the fourth leading cause of cancer-related death. GC is a multifactorial disease, where both environmental and genetic factors can have an impact on its occurrence and development. The incidence rate of GC rises progressively with age; the median age at diagnosis is 70 years. However, approximately 10% of gastric carcinomas are detected at the age of 45 or younger. Early-onset gastric cancer is a good model to study genetic alterations related to the carcinogenesis process, as young patients are less exposed to environmental carcinogens. Carcinogenesis is a multistage disease process specified by the progressive development of mutations and epigenetic alterations in the expression of various genes, which are responsible for the occurrence of the disease.

MSI and EBV Positive Gastric Cancer's Subgroups and Their Link With Novel Immunotherapy

Gastric cancers have been historically classified based on histomorphologic features. The Cancer Genome Atlas network reported the comprehensive identification of genetic alterations associated with gastric cancer, identifying four distinct subtypes- Epstein-Barr virus (EBV)-positive, microsatellite-unstable/instability (MSI), genomically stable and chromosomal instability. In particular, EBV-positive and MSI gastric cancers seem responsive to novel immunotherapies drugs. The aim of this review is to describe MSI and EBV positive gastric cancer's subgroups and their relationship with novel immunotherapy.

From biology to surgery: One step beyond histology for tailored surgical treatments of gastric cancer

Gastric cancer is the third most common cause of cancer related death. Although its incidence is globally declined, prognosis remains dismal in the Western hemisphere, while better outcomes are evidenced in Asian countries. Endoscopic or surgical resection with or without lymphadenectomy represents the only chance of cure, with limited improvements of the prognosis in case of associated chemotherapy in a neoadjuvant or adjuvant setting. This could be mainly attributed to the uniform fashion of treatment of gastric cancer, mainly based on the histological features, that usually do not reflect the complexity of the disease. With the recent introduction of genomic technologies and new generation sequencing techniques, gastric cancer biology is now investigated in great details. This has brought to the publication of three main molecular classifications, based on the underlying molecular biology of gastric cancer. Although only few clinical reports are currently present in literature, the identification of gastric cancer molecular subtypes has shown interesting findings that may pave the way to a tailored clinical and surgical management. The aim of this review is, thus, to give a comprehensive overview of the current molecular classifications as compared to the available histopathological ones, also focusing on the potential clinical and surgical benefits and the future perspectives for a more personalized treatment of gastric cancer.

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.

Microsatellite instability in gastric cancer: molecular bases, clinical perspectives, and new treatment approaches

Gastric cancer is one of the most aggressive malignancies, with limited treatment options in both locally advanced and metastatic setting, resulting in poor prognosis. Based on genomic characterization, stomach tumour has recently been described as a heterogeneous disease composed by different subtypes, each of them with peculiar molecular aspects and specific clinical behaviour. With an incidence of 22% among all western gastric tumour cases, stomach cancer with microsatellite instability was identified as one of these subgroups. Retrospective studies and limited prospective trials reported differences between gastric cancers with microsatellite stability and those with instability, mainly concerning clinical and pathological features, but also in regard to immunological microenvironment, correlation with prognostic value, and responses to treatment. In particular, gastric cancer with microsatellite instability constitutes a small but relevant subgroup associated with older age, female sex, distal stomach location, and lower number of lymph-node metastases. Emerging data attribute to microsatellite instability status a favourable prognostic meaning, whereas the poor outcomes reported after perioperative chemotherapy administration suggest a detrimental role of cytotoxic drugs in this gastric cancer subgroup. The strong immunogenicity and the widespread expression of immune-checkpoint ligands make microsatellite instability subtype more vulnerable to immunotherapeutic approach, e.g., with anti-PD-L1 and anti-CTLA4 antibodies. Since gastric cancer with microsatellite instability shows specific features and clinical behaviour not overlapping with microsatellite stable disease, microsatellite instability test might be suitable for inclusion in a diagnostic setting for all tumour stages to guarantee the most targeted and effective treatment to every patient.

The Pattern of Signatures in Gastric Cancer Prognosis

Gastric cancer is one of the most common malignancies worldwide and it is a fourth leading cause of cancer-related death. Carcinogenesis is a multistage disease process specified by the gradual procurement of mutations and epigenetic alterations in the expression of different genes, which finally lead to the occurrence of a malignancy. These genes have diversified roles regarding cancer development. Intracellular pathways are assigned to the expression of different genes, signal transduction, cell-cycle supervision, genomic stability, DNA repair, and cell-fate destination, like apoptosis, senescence. Extracellular pathways embrace tumour invasion, metastasis, angiogenesis. Altered expression patterns, leading the different clinical responses. This review highlights the list of molecular biomarkers that can be used for prognostic purposes and provide information on the likely outcome of the cancer disease in an untreated individual.