BackgroundDiffuse gastric cancer (DGC) is associated with the reduction or absence of the expression of the cell adhesion protein E-cadherin (encoded by the CDH1 gene). Molecular characteristics are less well described for mixed gastric cancer (MGC). The main somatic alterations that have been described in the CDH1 gene are mutations, loss of heterozygosity (LOH) and promoter methylation. The aim was to analyze CDH1 somatic alterations in Mexican patients with diffuse and mixed gastric cancer.MethodsWe searched for mutations in the CDH1 gene in tumor DNA from DGC (n = 13) and MGC (n = 7) patients by next generation sequencing (NGS). Validation of findings was performed using Sanger sequencing. LOH was analyzed using dinucleotide repeat markers surrounding the CDH1 gene, and methylation was investigated by DNA bisulfite conversion and sequencing. E-cadherin protein deficiency was analyzed by immunohistochemistry.ResultsSeventeen point variants were identified by NGS, 13 of them were validated by Sanger sequencing. Only 1/13 had not been previously reported (c.-137C > A), and 12/13 were already reported as polymorphisms. Two DGC cases presented LOH at the locus 16q22.1 (13.3%). CDH1 promoter methylation was positive in (7/11) 63.6% and (4/6) 66.6% of the cases with DGC and MGC, respectively. E-cadherin protein deficiency was observed in 58.3% of DGC cases while 100% in MGC cases.ConclusionsWhile no pathogenic somatic mutations were found that could explain the diffuse histology of gastric cancer in DGC and MGC, methylation was the most common somatic inactivation event of the CDH1 gene, and LOH was rare. The previously unreported c.-137C > A variant modify the CDH1 gene expression since it alters the binding sites for transcription factors.Electronic supplementary materialThe online version of this article (10.1186/s12885-019-5294-0) contains supplementary material, which is available to authorized users.

ABSTRACT. Gastric cancer (GC), the third leading cause of cancerrelated deaths in Mexico and worldwide, can be classified into diffuse (DGC) or intestinal (IGC) types based on its histological characteristics. DGC is characterized by reduced expression of the cell adhesion protein E-cadherin, which is encoded by CDH1. The -472delA (rs5030625) and -160C>A (rs16260) polymorphisms in CDH1 induce a decrease in gene transcription; in fact, these mutated alleles have been associated with GC in some populations, with conflicting results. The aim of this study was to determine the association between the CDH1 -472delA and -160C>A polymorphisms and DGC and IGC in Mexican patients. The study was conducted in 24, 23, 48, and 93 individuals with DGC and IGC, without GC (control), and belonging to the general Mexican population (GMP), respectively. The genotypes were obtained by polymerase chain reaction -restriction fragment length polymorphism and the obtained data analyzed using Arlequin 3.1. The frequencies of the mutated allele (A) of -472delA were 0.326, 0.318, 0.284, and 0.296 in the DGC, IGC, control, and GMP groups, respectively, and those of the -160C>A polymorphism were 0.174, 0.318, 0.313, and 0.280, respectively. The genotype and allele frequencies of the two polymorphisms did not differ significantly (P > 0.05) among DGC, IGC, and control subjects. Therefore, we concluded that the CDH1 -472delA and -160C>A polymorphisms are not associated with DGC or IGC in patients from western Mexico.

Gastric cancer (GC) is the third most lethal type of cancer worldwide. Single nucleotide polymorphisms (SNPs) in regulatory sites or coding regions can modify the expression of genes involved in gastric carcinogenesis, as ERBB2 , which encodes for the tyrosine-kinase receptor HER-2. The aim of this work was to analyze the association of the polymorphisms: rs2643194, rs2517951, rs2643195, rs2934971, and rs1058808 with GC, as they have not yet been analyzed in GC patients, as well as to report their frequency in the general Mexican population (GMP). We studied genomic DNA from subjects with GC (n=74), gastric inflammatory diseases (GID, n=76 control subjects), and GMP (n=102). Genotypes were obtained by means of real-time PCR and DNA-sequencing. The risks for GC were estimated through odds ratio (OR) using the Cochran-Armitage trend test and multinomial logistic regression. Increased risk for GC was observed under the dominant inheritance model for the rs2643194 TT or CT genotypes with an OR of 2.75 (95%CI 1.12−6.75, P=0.023); the rs2934971 TT or GT genotypes with an OR of 2.41 (95%CI 1.01−5.76, P=0.043), and the rs1058808 GG or CG genotypes with an OR of 2.21 (95%CI 1.00−4.87, P=0.046). The SNPs rs2643194, rs2934971, and rs1058808 of the ERBB2 gene were associated with increased risk for GC.