E-cadherin alterations in hereditary disorders with emphasis on hereditary diffuse gastric cancer

A 3D Computational Study on the Formation and Progression of Tumor Cells in Diffuse Gastric Cancer

Hereditary diffuse gastric cancer is characterized by an increased risk of diffuse gastric cancer and lobular breast cancer, and is caused by pathogenic germline variants of E-cadherin and α -E-catenin, which are key regulators of cell-cell adhesion. However, how the loss of cell-cell adhesion promotes cell dissemination remains to be fully understood. Therefore, a three-dimensional computer model was developed to describe the initial steps of diffuse gastric cancer development. In this model, we have implemented a cellular Potts approach that contemplates cell adhesion to other cells and to the extracellular matrix, cell extrusion from the gastric epithelia, and subsequent proliferation. We demonstrate that early disease features are determined by decreased adhesion of mutant cells to their normal epithelial neighbors, with concomitant increased attachment to matrix components. Importantly, our simulation shows how mechanical pressure and uncontrolled proliferation of mutant cells lead to modifications in cell shape and in gastric gland morphology. In conclusion, this work underscores the potential of computational models to elucidate the role of cellular and noncellular components in gastric cancer that may be relevant targets in therapeutic interventions.

Clinical approach for managing patients with unexpected CDH1 mutations: A case report

BACKGROUND

Hereditary diffuse gastric cancer (HDGC) (OMIM# 137215) is an autosomal dominant cancer syndrome associated with CDH1 (OMIM# 192090) mutations. Prophylactic total gastrectomy (PTG) is the most recommended preventive treatment when a pathogenic mutation is found. However, the increasing use of genetic testing has led to the identification of incidental CDH1 mutations in individuals without a family history of gastric cancer. It remains unclear whether these patients should undergo prophylactic total gastrectomy.

METHODS

Germline DNA, obtained from peripheral blood, was analysed by NGS.

RESULTS

A 47-year-old woman was diagnosed with high-grade serous ovarian carcinoma, FIGO stage IIIC, with a Homologous Recombination Deficiency (HRD) GIS status of 78 (positive, cut-off: 43). She received chemotherapy and niraparib treatment. A multigene panel test revealed no pathogenic mutations in BRCA1 (OMIM# 113705)/BRCA2 (OMIM# 600185) genes, but a de novo deletion of exon 16 in CDH1 was found incidentally. She had no previous family history of gastric or breast cancer. The patient was enrolled in a surveillance program involving periodic endoscopy and was diagnosed with diffuse gastric cancer through biopsies of a pale area in the antrum after 1 year of close endoscopic follow-up.

CONCLUSION

This case presents supportive evidence for the pathogenic classification of the loss of the last exon of CDH1.

Upper Gastrointestinal Cancers and the Role of Genetic Testing

Beyond the few established hereditary cancer syndromes with an upper gastrointestinal cancer component, there is increasing recognition of the contribution of novel pathogenic germline variants (gPVs) to upper gastrointestinal carcinogenesis. The detection of gPVs has potential implications for novel treatment approaches of the index cancer patient as well as long-term implications for surveillance and risk-reducing measures for cancer survivors and far-reaching implications for the patients' family. With widespread availability of multigene panel testing, new associations may be identified with germline-somatic integration being critical to determining true causality of novel gPVs. Comprehensive cancer care should incorporate both somatic and germline testing.

Novel breast cancer susceptibility loci under linkage peaks identified in African ancestry consortia

BACKGROUND

Expansion of genome-wide association studies across population groups is needed to improve our understanding of shared and unique genetic contributions to breast cancer. We performed association and replication studies guided by a priori linkage findings from African ancestry (AA) relative pairs.

METHODS

We performed fixed-effect inverse-variance weighted meta-analysis under three significant AA breast cancer linkage peaks (3q26-27, 12q22-23, and 16q21-22) in 9241 AA cases and 10 193 AA controls. We examined associations with overall breast cancer as well as estrogen receptor (ER)-positive and negative subtypes (193,132 SNPs). We replicated associations in the African-ancestry Breast Cancer Genetic Consortium (AABCG).

RESULTS

In AA women, we identified two associations on chr12q for overall breast cancer (rs1420647, OR = 1.15, p = 2.50×10-6; rs12322371, OR = 1.14, p = 3.15×10-6), and one for ER-negative breast cancer (rs77006600, OR = 1.67, p = 3.51×10-6). On chr3, we identified two associations with ER-negative disease (rs184090918, OR = 3.70, p = 1.23×10-5; rs76959804, OR = 3.57, p = 1.77×10-5) and on chr16q we identified an association with ER-negative disease (rs34147411, OR = 1.62, p = 8.82×10-6). In the replication study, the chr3 associations were significant and effect sizes were larger (rs184090918, OR: 6.66, 95% CI: 1.43, 31.01; rs76959804, OR: 5.24, 95% CI: 1.70, 16.16).

CONCLUSION

The two chr3 SNPs are upstream to open chromatin ENSR00000710716, a regulatory feature that is actively regulated in mammary tissues, providing evidence that variants in this chr3 region may have a regulatory role in our target organ. Our study provides support for breast cancer variant discovery using prioritization based on linkage evidence.

Genetic Basis of Breast and Ovarian Cancer: Approaches and Lessons Learnt from Three Decades of Inherited Predisposition Testing

Germline variants occurring in BRCA1 and BRCA2 give rise to hereditary breast and ovarian cancer (HBOC) syndrome, predisposing to breast, ovarian, fallopian tube, and peritoneal cancers marked by elevated incidences of genomic aberrations that correspond to poor prognoses. These genes are in fact involved in genetic integrity, particularly in the process of homologous recombination (HR) DNA repair, a high-fidelity repair system for mending DNA double-strand breaks. In addition to its implication in HBOC pathogenesis, the impairment of HR has become a prime target for therapeutic intervention utilizing poly (ADP-ribose) polymerase (PARP) inhibitors. In the present review, we introduce the molecular roles of HR orchestrated by BRCA1 and BRCA2 within the framework of sensitivity to PARP inhibitors. We examine the genetic architecture underneath breast and ovarian cancer ranging from high- and mid- to low-penetrant predisposing genes and taking into account both germline and somatic variations. Finally, we consider higher levels of complexity of the genomic landscape such as polygenic risk scores and other approaches aiming to optimize therapeutic and preventive strategies for breast and ovarian cancer.

The ECM and tissue architecture are major determinants of early invasion mediated by E-cadherin dysfunction

Germline mutations of E-cadherin cause Hereditary Diffuse Gastric Cancer (HDGC), a highly invasive cancer syndrome characterised by the occurrence of diffuse-type gastric carcinoma and lobular breast cancer. In this disease, E-cadherin-defective cells are detected invading the adjacent stroma since very early stages. Although E-cadherin loss is well established as a triggering event, other determinants of the invasive process persist largely unknown. Herein, we develop an experimental strategy that comprises in vitro extrusion assays using E-cadherin mutants associated to HDGC, as well as mathematical models epitomising epithelial dynamics and its interaction with the extracellular matrix (ECM). In vitro, we verify that E-cadherin dysfunctional cells detach from the epithelial monolayer and extrude basally into the ECM. Through phase-field modelling we demonstrate that, aside from loss of cell-cell adhesion, increased ECM attachment further raises basal extrusion efficiency. Importantly, by combining phase-field and vertex model simulations, we show that the cylindrical structure of gastric glands strongly promotes the cell's invasive ability. Moreover, we validate our findings using a dissipative particle dynamics simulation of epithelial extrusion. Overall, we provide the first evidence that cancer cell invasion is the outcome of defective cell-cell linkages, abnormal interplay with the ECM, and a favourable 3D tissue structure.

Hereditary Diffuse Gastric Cancer: Molecular Genetics, Biological Mechanisms and Current Therapeutic Approaches

Hereditary diffuse gastric cancer is an autosomal dominant syndrome characterized by a high prevalence of diffuse gastric cancer and lobular breast cancer. It is caused by inactivating mutations in the tumor suppressor gene CDH1. Genetic testing technologies have become more efficient over the years, also enabling the discovery of other susceptibility genes for gastric cancer, such as CTNNA1 among the most important genes. The diagnosis of pathogenic variant carriers with an increased risk of developing gastric cancer is a selection process involving a multidisciplinary team. To achieve optimal long-term results, it requires shared decision-making in risk management. In this review, we present a synopsis of the molecular changes and current therapeutic approaches in HDGC based on the current literature.

Collective mechanical responses of cadherin-based adhesive junctions as predicted by simulations

Cadherin-based adherens junctions and desmosomes help stabilize cell-cell contacts with additional function in mechano-signaling, while clustered protocadherin junctions are responsible for directing neuronal circuits assembly. Structural models for adherens junctions formed by epithelial cadherin (CDH1) proteins indicate that their long, curved ectodomains arrange to form a periodic, two-dimensional lattice stabilized by tip-to-tip trans interactions (across junction) and lateral cis contacts. Less is known about the exact architecture of desmosomes, but desmoglein (DSG) and desmocollin (DSC) cadherin proteins are also thought to form ordered junctions. In contrast, clustered protocadherin (PCDH)-based cell-cell contacts in neuronal tissues are thought to be responsible for self-recognition and avoidance, and structural models for clustered PCDH junctions show a linear arrangement in which their long and straight ectodomains form antiparallel overlapped trans complexes. Here, we report all-atom molecular dynamics simulations testing the mechanics of minimalistic adhesive junctions formed by CDH1, DSG2 coupled to DSC1, and PCDHγB4, with systems encompassing up to 3.7 million atoms. Simulations generally predict a favored shearing pathway for the adherens junction model and a two-phased elastic response to tensile forces for the adhesive adherens junction and the desmosome models. Complexes within these junctions first unbend at low tensile force and then become stiff to unbind without unfolding. However, cis interactions in both the CDH1 and DSG2-DSC1 systems dictate varied mechanical responses of individual dimers within the junctions. Conversely, the clustered protocadherin PCDHγB4 junction lacks a distinct two-phased elastic response. Instead, applied tensile force strains trans interactions directly, as there is little unbending of monomers within the junction. Transient intermediates, influenced by new cis interactions, are observed after the main rupture event. We suggest that these collective, complex mechanical responses mediated by cis contacts facilitate distinct functions in robust cell-cell adhesion for classical cadherins and in self-avoidance signaling for clustered PCDHs.

Germline CDH1 G212E Missense Variant: Combining Clinical, In Vitro and In Vivo Strategies to Unravel Disease Burden

Simple Summary

Hereditary diffuse gastric cancer (HDGC) is an inherited cancer syndrome associated with CDH1 germline mutations. The increasing detection of CDH1 genetic variants due to multigene panel testing poses a serious clinical challenge and urges the development of effective classification strategies. In this study, we describe the identification of the novel CDH1 G212E variant in a large family strongly affected by diffuse gastric cancer. Through a comprehensive characterization pipeline, we provide evidence of the damaging nature of this genetic alteration, thus impacting patient management and family screening.

Abstract

E-cadherin, encoded by CDH1, is an essential molecule for epithelial homeostasis, whose loss or aberrant expression results in disturbed cell–cell adhesion, increased cell invasion and metastasis. Carriers of CDH1 germline mutations have a high risk of developing diffuse gastric cancer and lobular breast cancer, associated with the cancer syndrome Hereditary Diffuse Gastric Cancer (HDGC). The ubiquitous availability of cancer panels has led to the identification of an increasing amount of “incidental” CDH1 genetic variants that pose a serious clinical challenge. This has sparked intensive research aiming at an accurate classification of the variants and consequent validation of their clinical relevance. The present study addressed the significance of a novel CDH1 variant, G212E, identified in an unusually large pedigree displaying strong aggregation of diffuse gastric cancer. We undertook a comprehensive pipeline encompassing family data, in silico predictions, in vitro assays and in vivo strategies, which validated the deleterious phenotype induced by this genetic alteration. In particular, we demonstrated that the G212E variant affects the stability and localization, as well as the adhesive and anti-invasive functions of E-cadherin, triggering epithelial disruption and disorganization. Our findings illustrate the clinical implication of a complementary approach for effective variant categorization and patient management.

Primary Signet Ring Cell/Histiocytoid Carcinoma of the Eyelid: Somatic Mutations in CDH1 and Other Clinically Actionable Mutations Imply Early Use of Targeted Agents

Primary signet ring cell/histiocytoid carcinoma of the eyelid is a rare ocular malignancy and its diagnosis is often delayed. This neoplasm presents as an insidious, diffusely infiltrative mass in the periocular area that later infiltrates the orbit. An exenteration is usually indicated; however, nearly one-third of patients develop local recurrence or metastasis. Morphologically, it resembles signet ring cell carcinoma of the stomach and breast, raising the possibility of mutations in CDH1, the gene encoding E-cadherin. To determine whether primary signet ring cell/histiocytoid carcinoma harbors the CDH1 mutation or other actionable mutations, we analyzed the tumor tissue via next-generation sequencing. We identified only one case of primary signet ring cell carcinoma of the eyelid with adequate DNA quality for sequencing from the pathological archive during the period 2000 to 2020. A comprehensive evaluation including histopathology, immunohistochemistry, and next-generation sequencing assay was performed on tumor tissue. Immunohistochemically, the tumor exhibited E-cadherin membranous staining with the aberrant cytoplasmic staining of β-catenin. Using next-generation sequencing, we demonstrated the mutation in the CDH1 gene. In addition, other clinically actionable mutations including ERBB2 and PIK3CA were also detected. The alterations in other actionable genes indicate a need for larger studies to evaluate the pathogenesis and potential therapies for primary signet ring cell/histiocytoid carcinoma of the eyelid.

Associations of CDH1 germline variant location and cancer phenotype in families with hereditary diffuse gastric cancer (HDGC)

INTRODUCTION

Hereditary diffuse gastric cancer (HDGC) is a cancer syndrome associated with variants in E-cadherin (CDH1), diffuse gastric cancer and lobular breast cancer. There is considerable heterogeneity in its clinical manifestations. This study aimed to determine associations between CDH1 germline variant status and clinical phenotypes of HDGC.

METHODS

One hundred and fifty-two HDGC families, including six previously unreported families, were identified. CDH1 gene-specific guidelines released by the Clinical Genome Resource (ClinGen) CDH1 Variant Curation Expert Panel were applied for pathogenicity classification of truncating, missense and splice site CDH1 germline variants. We evaluated ORs between location of truncating variants of CDH1 and incidence of colorectal cancer, breast cancer and cancer at young age (gastric cancer at <40 or breast cancer <50 years of age).

RESULTS

Frequency of truncating germline CDH1 variants varied across functional domains of the E-cadherin receptor gene and was highest in linker (0.05785 counts/base pair; p=0.0111) and PRE regions (0.10000; p=0.0059). Families with truncating CDH1 germline variants located in the PRE-PRO region were six times more likely to have family members affected by colorectal cancer (OR 6.20, 95% CI 1.79 to 21.48; p=0.004) compared with germline variants in other regions. Variants in the intracellular E-cadherin region were protective for cancer at young age (OR 0.2, 95% CI 0.06 to 0.64; p=0.0071) and in the linker regions for breast cancer (OR 0.35, 95% CI 0.12 to 0.99; p=0.0493). Different CDH1 genotypes were associated with different intracellular signalling activation levels including different p-ERK, p-mTOR and β-catenin levels in early submucosal T1a lesions of HDGC families with different CDH1 variants.

CONCLUSION

Type and location of CDH1 germline variants may help to identify families at increased risk for concomitant cancers that might benefit from individualised surveillance and intervention strategies.

The significance of gene mutations across eight major cancer types

Mutations occur spontaneously, which can be induced by either chemicals (e.g. benzene) or biological factors (e.g. virus). Not all mutations cause noticeable changes in cellular functions. However, mutation in key cellular genes leads to developmental disorders. It is one of the main ways in which proto-oncogenes can be changed into their oncogenic state. The progressive accumulation of multiple mutations throughout life leads to cancer. In the past few decades, extensive research on cancer biology has discovered many genes and pathways having role in cancer development. In this review, we tried to summarize the current knowledge of mutational effect on different cancer types and its consequences in brief for future reference and guidance of researchers in cancer biology.

Clinical spectrum and pleiotropic nature of CDH1 germline mutations

CDH1 encodes E-cadherin, a key protein in adherens junctions. Given that E-cadherin is involved in major cellular processes such as embryogenesis and maintenance of tissue architecture, it is no surprise that deleterious effects arise from its loss of function. E-cadherin is recognised as a tumour suppressor gene, and it is well established that CDH1 genetic alterations cause diffuse gastric cancer and lobular breast cancer—the foremost manifestations of the hereditary diffuse gastric cancer syndrome. However, in the last decade, evidence has emerged demonstrating that CDH1 mutations can be associated with lobular breast cancer and/or several congenital abnormalities, without any personal or family history of diffuse gastric cancer. To date, no genotype–phenotype correlations have been observed. Remarkably, there are reports of mutations affecting the same nucleotide but inducing distinct clinical outcomes. In this review, we bring together a comprehensive analysis of CDH1-associated disorders and germline alterations found in each trait, providing important insights into the biological mechanisms underlying E-cadherin’s pleiotropic effects. Ultimately, this knowledge will impact genetic counselling and will be relevant to the assessment of risk of cancer development or congenital malformations in CDH1 mutation carriers.

Diffuse Gastric Cancer: A Summary of Analogous Contributing Factors for Its Molecular Pathogenicity

Gastric cancer is the third leading cause of cancer-related deaths and ranks as the fifth most common cancer worldwide. Incidence and mortality differ depending on the geographical region and gastric cancer ranks first in East Asian countries. Although genetic factors, gastric environment, and Helicobacter pylori infection have been associated with the pathogenicity and development of intestinal-type gastric cancer that follows the Correa’s cascade, the pathogenicity of diffuse-type gastric cancer remains mostly unknown and undefined. However, genetic abnormalities in the cell adherence factors, such as E-cadherin and cellular activities that cause impaired cell integrity and physiology, have been documented as contributing factors. In recent years, H. pylori infection has been also associated with the development of diffuse-type gastric cancer. Therefore, in this report, we discuss the host factors as well as the bacterial factors that have been reported as associated factors contributing to the development of diffuse-type gastric cancer.

Therapeutic and prophylactic gastrectomy in a family with hereditary diffuse gastric cancer secondary to a CDH1 mutation: a case series

BACKGROUND

Gastric cancer is the fifth most prevalent and the third most lethal cancer worldwide, causing approximately 720,000 deaths annually. Although most cases of gastric cancers are sporadic, one of its inherited forms, hereditary diffuse gastric cancer (HDGC), constitutes about 1-3% of cases. Interestingly, females in families with HDGC are also predisposed to developing lobular breast cancer (LBC). Recent analyses have identified loss-of-function germline mutations in cadherein-1 (CDH1) as a culprit in HDGC and LBC. This discovery fueled several sequencing analyses and case series reports analyzing the pattern of inheritance of CDH1 and its propensity to induce HDGC. In 2015, a multinational and multidisciplinary task force updated the guidelines and criteria for screening, diagnosing, and managing HDGC.

CASE PRESENTATION

Here, we present a case series of three siblings with family history of HDGC who tested positive for the CDH1 mutation and describe their surgical treatment course, post-operative management, and follow-up as they pertain to the updated guidelines.

CONCLUSIONS

Despite recent updates in guidelines in the diagnosis and management of HDGC, the disease remains challenging to address with patients given the high level of uncertainty and the comorbidities associated with prophylactic intervention. We strongly recommend that an interdisciplinary team inclusive of clinical and surgical oncologists, along with geneticists, social work, and psychological support, should follow the patients in a longitudinal and comprehensive manner in order to achieve full recovery and return to normalcy, as with our patients.

Association between hOGG1 polymorphism rs1052133 and gastric cancer

Purpose

To conduct a comprehensive evaluation of the association of the human8-oxoguanine glycosylase 1 (hOGG1) gene polymorphism rs1052133 with gastric cancer (GC) through a systematic review and meta-analysis of genetic association study.

Results

A total of 15 articles from published papers were included in our analysis. The meta-analyses for hOGG1 rs1052133, composed of 4024GC patients and 6022controls, showed low heterogeneity for the included populations in all the genetic models, except for the Caucasian population under allelic genetic model, the Asian population under addictive model and Caucasian population under dominant model. The analyses of all the genetic models in overall pooled populations did not identify any significant association between GC and hOGG1 rs1052133 (Allelic model: C vs. G, p = 0.746; Addictive model: CC vs. GG, p = 0.888; Recessive model: CC +GC vs. GG, p = 0.628; Dominant model: CC vs. GG+GC, p = 0.147), even though stratified analyses were conducted in different ethnicities under each genetic model.

Materials and Methods

All case-control association studies on hOGG1 and GC reported up to December 15, 2016 in PubMed, Embase, Web of Science, and the Chinese Biomedical Database were retrieved. Odds ratios (ORs) and 95% confidence intervals (95% CIs) were calculated for single-nucleotide polymorphism (SNP) using fixed- and random- effects models according to between-study heterogeneity. Publication bias analyses were conducted using Begg test.

Conclusions

This meta-analysis showed there was no association between hOGG1 rs1052133 and GC. Given the limited sample size, further investigations including more ethnic groups are required to validate the association.

Predicting the Functional Impact of CDH1 Missense Mutations in Hereditary Diffuse Gastric Cancer

The role of E-cadherin in Hereditary Diffuse Gastric Cancer (HDGC) is unequivocal. Germline alterations in its encoding gene (CDH1) are causative of HDGC and occur in about 40% of patients. Importantly, while in most cases CDH1 alterations result in the complete loss of E-cadherin associated with a well-established clinical impact, in about 20% of cases the mutations are of the missense type. The latter are of particular concern in terms of genetic counselling and clinical management, as the effect of the sequence variants in E-cadherin function is not predictable. If a deleterious variant is identified, prophylactic surgery could be recommended. Therefore, over the last few years, intensive research has focused on evaluating the functional consequences of CDH1 missense variants and in assessing E-cadherin pathogenicity. In that context, our group has contributed to better characterize CDH1 germline missense variants and is now considered a worldwide reference centre. In this review, we highlight the state of the art methodologies to categorize CDH1 variants, as neutral or deleterious. This information is subsequently integrated with clinical data for genetic counseling and management of CDH1 variant carriers.

Linear-Stapled Side-to-Side Esophagojejunostomy with Hand-Sewn Closure of the Common Enterotomy After Prophylactic and Therapeutic Total Gastrectomy

After total gastrectomy, anastomosis-related complications such as leak or stricture can be highly morbid. Between July 2005 and December 2015, a linear-stapled side-to-side esophagojejunostomy with hand-sewn closure of the common enterotomy (modified Orringer technique) was used for Roux-en-Y reconstruction after prophylactic total gastrectomy in 22 germline CDH1 mutation carriers and after therapeutic total gastrectomy in 18 patients diagnosed with gastric adenocarcinoma. All operations were performed by the same surgeon. No patient in either cohort developed a clinically evident anastomotic leak, one patient (2.5%) developed a contained radiographic leak that healed without intervention, and one patient (2.5%) developed an anastomotic stricture treated by endoscopic dilatation 7 months after operation. These rates were lower than radiographic leak and stricture rates in a comparison group of 32 patients who received a completely hand-sewn esophagojejunostomy (6.3 and 3.1%, respectively). Here, we describe how to perform the linear-stapled esophagojejunostomy anastomosis.

Quantification of topological features in cell meshes to explore E-cadherin dysfunction

In cancer, defective E-cadherin leads to cell detachment, migration and metastization. Further, alterations mediated by E-cadherin dysfunction affect cell topology and tissue organization. Herein, we propose a novel quantitative approach, based on microscopy images, to analyse abnormal cellular distribution patterns. We generated undirected graphs composed by sets of triangles which accurately reproduce cell positioning and structural organization within each image. Network analysis was developed by exploring triangle geometric features, namely area, edges length and formed angles, as well as their variance, when compared with the respective equilateral triangles. We generated synthetic networks, mimicking the diversity of cell-cell interaction patterns, and evaluated the applicability of the selected metrics to study topological features. Cells expressing wild-type E-cadherin and cancer-related mutants were used to validate our strategy. Specifically, A634V, R749W and P799R cancer-causing mutants present more disorganized spatial distribution when compared with wild-type cells. Moreover, P799R exhibited higher length and angle distortions and abnormal cytoskeletal organization, suggesting the formation of very dynamic and plastic cellular interactions. Hence, topological analysis of cell network diagrams is an effective tool to quantify changes in cell-cell interactions and, importantly, it can be applied to a myriad of processes, namely tissue morphogenesis and cancer.

Molecular alterations in gastric cancer with special reference to the early-onset subtype

Currently, gastric cancer (GC) is one of the most frequently diagnosed neoplasms, with a global burden of 723000 deaths in 2012. It is the third leading cause of cancer-related death worldwide. There are numerous possible factors that stimulate the pro-carcinogenic activity of important genes. These factors include genetic susceptibility expressed in a single-nucleotide polymorphism, various acquired mutations (chromosomal instability, microsatellite instability, somatic gene mutations, epigenetic alterations) and environmental circumstances (e.g., Helicobcter pylori infection, EBV infection, diet, and smoking). Most of the aforementioned pathways overlap, and authors agree that a clear-cut pathway for GC may not exist. Thus, the categorization of carcinogenic events is complicated. Lately, it has been claimed that research on early-onset gastric carcinoma (EOGC) and hereditary GC may contribute towards unravelling some part of the mystery of the GC molecular pattern because young patients are less exposed to environmental carcinogens and because carcinogenesis in this setting may be more dependent on genetic factors. The comparison of various aspects that differ and coexist in EOGCs and conventional GCs might enable scientists to: distinguish which features in the pathway of gastric carcinogenesis are modifiable, discover specific GC markers and identify a specific target. This review provides a summary of the data published thus far concerning the molecular characteristics of GC and highlights the outstanding features of EOGC.

Familial gastric cancer: genetic susceptibility, pathology, and implications for management

Familial gastric cancer comprises at least three major syndromes: hereditary diffuse gastric cancer, gastric adenocarcinoma and proximal polyposis of the stomach, and familial intestinal gastric cancer. The risk of development of gastric cancer is high in families affected b-y these syndromes, but only hereditary diffuse gastric cancer is genetically explained (caused by germline alterations of CDH1, which encodes E-cadherin). Gastric cancer is also associated with a range of several cancer-associated syndromes with known genetic causes, such as Lynch, Li-Fraumeni, Peutz-Jeghers, hereditary breast-ovarian cancer syndromes, familial adenomatous polyposis, and juvenile polyposis. We present contemporary knowledge on the genetics, pathogenesis, and clinical features of familial gastric cancer, and discuss research and technological developments, which together are expected to open avenues for new genetic testing approaches and novel therapeutic strategies.

Prophylactic total gastrectomy in hereditary diffuse gastric cancer: identification of two novel CDH1 gene mutations-a clinical observational study

Inactivating mutations in the CDH1 (E-cadherin) gene are the predisposing cause of gastric cancer in most families with hereditary diffuse gastric cancer (HDGC). The lifetime risk of cancer in mutation positive members is more than 80 % and prophylactic total gastrectomy is recommended. Not all mutations in the CDH1 gene are however pathogenic and it is important to classify mutations before this major operation is performed. Probands from two Danish families with gastric cancer and a history suggesting HDGC were screened for CDH1 gene mutations. Two novel CDH1 gene mutations were identified and found pathogenic. In silico and mini-gene assay were used to predict the functional consequence in one of them. Mutation carriers were offered endoscopy and total gastrectomy. The gastric specimens were completely sectioned and examined histologically. Seven asymptomatic mutation carriers were operated. Hospital stay was 6-8 days and there were no complications. Small foci of diffuse gastric cancer were found in all patients-intramucosal in six and advanced in one. Preoperative endoscopic biopsies had revealed a microscopic cancer focus in two of the patients. Our data confirmed the pathogenic nature of both mutations and strongly support the recommendation of total gastrectomy in asymptomatic CDH1 gene mutation carriers. The functional consequences of novel CDH1 gene mutations with uncertain effects should be tested before correct advice and treatment can be given.

Putative linkage signals identified for breast cancer in African American families

BACKGROUND

Genome-wide association studies have identified polymorphisms associated with breast cancer subtypes and across multiple population subgroups; however, few studies to date have applied linkage analysis to other population groups.

METHODS

We performed the first genome-wide breast cancer linkage analysis in 106 African American families (comprising 179 affected and 79 unaffected members) not known to be segregating BRCA mutations to search for novel breast cancer loci. We performed regression-based model-free multipoint linkage analyses of the sibling pairs using SIBPAL, and two-level Haseman-Elston linkage analyses of affected relative pairs using RELPAL.

RESULTS

We identified -log10 P values that exceed 4 on chromosomes 3q and 12q, as well as a region near BRCA1 on chromosome 17 (-log10 P values in the range of 3.0-3.2) using both sibling-based and relative-based methods; the latter observation may suggest that undetected BRCA1 mutations or other mutations nearby such as HOXB13 may be segregating in our sample.

CONCLUSIONS

In summary, these results suggest novel putative regions harboring risk alleles in African Americans that deserve further study.

IMPACT

We hope that our study will spur further family-based investigation into specific mechanisms for breast cancer disparities.

Hereditary diffuse gastric cancer - pathophysiology and clinical management

Hereditary Diffuse Gastric Cancer is an autosomal dominant inherited gastric cancer syndrome caused by germline alterations in CDH1 (E-cadherin) and CTNNA1 (alpha-E-catenin) genes. Germline CDH1 alterations encompass small frameshifts, splice-site, nonsense, and missense mutations, as well as large rearrangements. Most CDH1 truncating mutations are pathogenic, and several missense CDH1 mutations have a deleterious effect on E-cadherin function. CDH1 testing should be performed in probands. Screening of at-risk individuals is indicated from the age of consent following counselling with a multidisciplinary team. In mutation-positive individuals prophylactic gastrectomy is recommended. Endoscopic surveillance is an option for those refusing/postponing gastrectomy, those with mutations of undetermined significance, and in CDH1-negative families. Ongoing research focus on the search of genetic causes other than CDH1 or CTNNA1 germline defects; assessment of the pathogenicity and penetrance of CDH1 missense mutations and identification of somatic mechanisms behind the progression from early (indolent) lesions to invasive (lethal) carcinomas.

E-cadherin germline mutation carriers: clinical management and genetic implications

Hereditary diffuse gastric cancer is an autosomic dominant syndrome associated with E-cadherin protein (CDH1) gene germline mutations. Clinical criteria for genetic screening were revised in 2010 by the International Gastric Cancer Linkage Consortium at the Cambridge meeting. About 40 % of families fulfilling clinical criteria for this inherited disease present deleterious CDH1 germline mutations. Lobular breast cancer is a neoplastic condition associated with hereditary diffuse gastric cancer syndrome. E-cadherin constitutional mutations have been described in both settings, in gastric and breast cancers. The management of CDH1 asymptomatic mutation carriers requires a multidisciplinary approach; the only life-saving procedure is the prophylactic total gastrectomy after thorough genetic counselling. Several prophylactic gastrectomies have been performed to date; conversely, no prophylactic mastectomies have been described in CDH1 mutant carriers. However, the recent discovery of novel germline alterations in pedigree clustering only for lobular breast cancer opens up a new debate in the management of these individuals. In this critical review, we describe the clinical management of CDH1 germline mutant carriers providing specific recommendations for genetic counselling, clinical criteria, surveillance and/ or prophylactic surgery.

Genetics of gastric cancer

Gastric cancer remains highly prevalent and accounts for a notable proportion of global cancer mortality. This cancer is also associated with poor survival rates. Understanding the genetic basis of gastric cancer will offer insights into its pathogenesis, help identify new biomarkers and novel treatment targets, aid prognostication and could be central to developing individualized treatment strategies in the future. An inherited component contributes to <3% of gastric cancers; the majority of genetic changes associated with gastric cancer are acquired. Over the past few decades, advances in technology and high-throughput analysis have improved understanding of the molecular aspects of the pathogenesis of gastric cancer. These aspects are multifaceted and heterogeneous and represent a wide spectrum of several key genetic influences, such as chromosomal instability, microsatellite instability, changes in microRNA profile, somatic gene mutations or functional single nucleotide polymorphisms. These genetic aspects of the pathogenesis of gastric cancer will be addressed in this Review.

Genetic screening analysis of patients with hereditary diffuse gastric cancer from northern and northeastern Brazil

Background

Hereditary diffuse gastric cancer (HDGC) is a hereditary autosomal inherited syndrome associated with CDH1 germline mutations. In Brazil, gastrointestinal tumors are among the most prevalent tumor types and constitute a serious public health problem, especially in the northern and northeastern regions. This study aimed to investigate germline mutations, methylation pattern and genomic rearrangements in the CDH1 gene and quantitative changes in the DNA of HDGC patients in northern and northeastern Brazil.

Methods

Twenty-seven DNA samples from the members of four families affected by HDGC were analyzed using array comparative genomic hybridization (aCGH), DNA sequencing and methylation pattern.

Results

No evidence of gain and loss events or any rearrangements were found in any of the samples tested using aCGH. No promoter region hypermethylation was observed either. Two of the four families presented different types of germline mutations. The 185G > T and 1018A > G germline mutations detected in this study have been described in Asian and European families, respectively. The ancestors of the two families carrying these mutations had originated from those continents.

Conclusion

This is the first study to evaluate CDH1 gene germline mutations in Brazilian families with HDGC. In our study, 50% of the families showed no CDH1 gene alterations, and it is possible that in regions with a high incidence of gastric cancer, such as northern and northeastern Brazil, environmental factors might have induced the different genetic alterations analyzed in this study.

Pattern-recognition receptors and gastric cancer

Chronic inflammation has been associated with an increased risk of several human malignancies, a classic example being gastric adenocarcinoma (GC). Development of GC is known to result from infection of the gastric mucosa by Helicobacter pylori, which initially induces acute inflammation and, in a subset of patients, progresses over time to chronic inflammation, gastric atrophy, intestinal metaplasia, dysplasia, and finally intestinal-type GC. Germ-line encoded receptors known as pattern-recognition receptors (PRRs) are critical for generating mature pro-inflammatory cytokines that are crucial for both Th1 and Th2 responses. Given that H. pylori is initially targeted by PRRs, it is conceivable that dysfunction within genes of this arm of the immune system could modulate the host response against H. pylori infection, and subsequently influence the emergence of GC. Current evidence suggests that Toll-like receptors (TLRs) (TLR2, TLR3, TLR4, TLR5, and TLR9), nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs) (NOD1, NOD2, and NLRP3), a C-type lectin receptor (DC-SIGN), and retinoic acid-inducible gene (RIG)-I-like receptors (RIG-I and MDA-5), are involved in both the recognition of H. pylori and gastric carcinogenesis. In addition, polymorphisms in genes involved in the TLR (TLR1, TLR2, TLR4, TLR5, TLR9, and CD14) and NLR (NOD1, NOD2, NLRP3, NLRP12, NLRX1, CASP1, ASC, and CARD8) signaling pathways have been shown to modulate the risk of H. pylori infection, gastric precancerous lesions, and/or GC. Further, the modulation of PRRs has been suggested to suppress H. pylori-induced inflammation and enhance GC cell apoptosis, highlighting their potential relevance in GC therapeutics. In this review, we present current advances in our understanding of the role of the TLR and NLR signaling pathways in the pathogenesis of GC, address the involvement of other recently identified PRRs in GC, and discuss the potential implications of PRRs in GC immunotherapy.

Genomic profile analysis of diffuse-type gastric cancers

BACKGROUND

Stomach cancer is the third deadliest among all cancers worldwide. Although incidence of the intestinal-type gastric cancer has decreased, the incidence of diffuse-type is still increasing and its progression is notoriously aggressive. There is insufficient information on genome variations of diffuse-type gastric cancer because its cells are usually mixed with normal cells, and this low cellularity has made it difficult to analyze the genome.

RESULTS

We analyze whole genomes and corresponding exomes of diffuse-type gastric cancer, using matched tumor and normal samples from 14 diffuse-type and five intestinal-type gastric cancer patients. Somatic variations found in the diffuse-type gastric cancer are compared to those of the intestinal-type and to previously reported variants. We determine the average exonic somatic mutation rate of the two types. We find associated candidate driver genes, and identify seven novel somatic mutations in CDH1, which is a well-known gastric cancer-associated gene. Three-dimensional structure analysis of the mutated E-cadherin protein suggests that these new somatic mutations could cause significant functional perturbations of critical calcium-binding sites in the EC1-2 junction. Chromosomal instability analysis shows that the MDM2 gene is amplified. After thorough structural analysis, a novel fusion gene TSC2-RNF216 is identified, which may simultaneously disrupt tumor-suppressive pathways and activate tumorigenesis.

CONCLUSIONS

We report the genomic profile of diffuse-type gastric cancers including new somatic variations, a novel fusion gene, and amplification and deletion of certain chromosomal regions that contain oncogenes and tumor suppressors.

Unmet needs and challenges in gastric cancer: the way forward

Although the incidence of gastric cancer has fallen steadily in developed countries over the past 50 years, outcomes in Western countries remain poor, primarily due to the advanced stage of the disease at presentation. While earlier diagnosis would help to improve outcomes for patients with gastric cancer, better understanding of the biology of the disease is also needed, along with advances in therapy. Indeed, progress in the treatment of gastric cancer has been limited, mainly because of its genetic complexity and heterogeneity. As a result, there is an urgent need to apply precision medicine to the management of the disease in order to ensure that individuals receive the most appropriate treatment. This article suggests a number of strategies that may help to accelerate progress in treating patients with gastric cancer. Incorporation of some of these approaches could help to improve the quality of life and survival for patients diagnosed with the disease. Standardisation of care across Europe through expansion of the European Registration of Cancer Care (EURECCA) registry - a European cancer audit that aims to improve quality and decrease variation in care across the region - may also be expected to lead to improved outcomes for those suffering from this common malignancy.

Beyond E-cadherin: roles of other cadherin superfamily members in cancer

Loss of cadherin 1 (CDH1; also known as epithelial cadherin (E-cadherin)) is used for the diagnosis and prognosis of epithelial cancers. However, it should not be ignored that the superfamily of transmembrane cadherin proteins encompasses more than 100 members in humans, including other classical cadherins, numerous protocadherins and cadherin-related proteins. Elucidation of their roles in suppression versus initiation or progression of various tumour types is a young but fascinating field of molecular cancer research. These cadherins are very diverse in both structure and function, and their mutual interactions seem to influence biological responses in complex and versatile ways.

Rescue of wild-type E-cadherin expression from nonsense-mutated cancer cells by a suppressor-tRNA

Hereditary diffuse gastric cancer (HDGC) syndrome, although rare, is highly penetrant at an early age, and is severe and incurable because of ineffective screening tools and therapy. Approximately 45% of HDGC families carry germline CDH1/E-cadherin alterations, 20% of which are nonsense leading to premature protein truncation. Prophylactic gastrectomy is the only recommended approach for all asymptomatic CDH1 mutation carriers. Suppressor-tRNAs can replace premature stop codons (PTCs) with a cognate amino acid, inducing readthrough and generating full-length proteins. The use of suppressor-tRNAs in HDGC patients could therefore constitute a less invasive therapeutic option for nonsense mutation carriers, delaying the development of gastric cancer. Our analysis revealed that 23/108 (21.3%) of E-cadherin-mutant families carried nonsense mutations that could be potentially corrected by eight suppressor-tRNAs, and arginine was the most frequently affected amino acid. Using site-directed mutagenesis, we developed an arginine suppressor-tRNA vector to correct one HDGC nonsense mutation. E-cadherin- deficient cell lines were transfected with plasmids carrying simultaneously the suppressor-tRNA and wild-type or mutant CDH1 mini-genes. RT-PCR, western blot, immunofluorescence, flow cytometry and proximity ligation assay (PLA) were used to establish the model, and monitor mRNA and protein expression and function recovery from CDH1 vectors. Cells expressing a CDH1 mini-gene, carrying a nonsense mutation and the suppressor-tRNA, recovered full-length E-cadherin expression and its correct localization and incorporation into the adhesion complex. This is the first demonstration of functional recovery of a mutated causative gene in hereditary cancer by cognate amino acid replacement with suppressor-tRNAs. Of the HDGC families, 21.3% are candidates for correction with suppressor-tRNAs to potentially delay cancer onset.

Multiplex genetic cancer testing identifies pathogenic mutations in TP53 and CDH1 in a patient with bilateral breast and endometrial adenocarcinoma

Background

Germline genetic testing for familial cancer syndromes is usually performed serially for the most likely genetic causes. In recent years the way genetic testing carried out has changed, as next generation sequencing now allows the simultaneous testing of multiple susceptibility genes at low costs.

Case presentation

Here, we present a female with bilateral breast cancer and endometrial adenocarcinoma. After simultaneous sequencing of 150 genes (890 kb) associated with hereditary cancer we identified pathogenic mutations in two high-penetrance genes, i.e. TP53 and CDH1 that would most likely not have been elucidated by serial screening of candidate genes.

Conclusion

As the two mutated genes are located on different chromosomes and cause different cancer syndromes these findings had a tremendous impact not only on genetic counseling of the index patient and her family but also on subsequent surveillance strategies.