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Clinicopathological and molecular alterations in early gastric cancers with the microsatellite instability-high phenotype.

ABSTRACT: The relevance of the clinicopathological and molecular features of early gastric cancers (EGCs) having the microsatellite instability (MSI)-high phenotype has not been clearly defined in sporadic gastric carcinogenesis. Here, we examined the clinicopathological and molecular characteristics of EGC according to MSI status in 330 patients with EGC (intestinal-type adenocarcinoma). Tumors were classified as MSI-high (45 cases), MSI-low (9 cases), or microsatellite stable (MSS; 276 cases). The specimens were examined using a combination of polymerase chain reaction (PCR)-microsatellite assays and PCR-pyrosequencing to detect chromosomal allelic imbalances in multiple cancer-related chromosomal loci, MSI, gene mutations (KRAS and BRAF) and methylation status [high methylation epigenome (HME), intermediate methylation epigenome and low methylation epigenome]. In addition, the expression levels of various target proteins were examined using immunohistochemistry. Interestingly, EGC with the MSI phenotype showed distinct papillary features. The expression of gastric mucin was more frequent in EGC with the MSI phenotype, while p53 overexpression was common in EGCs, irrespective of MSI status. The frequency of HME was significantly higher in EGCs with the MSI phenotype than in EGCs with the MSS phenotype. Although there was a low frequency of allelic imbalance in EGCs with the MSI phenotype, some markers of allelic imbalance were more frequently detected in EGCs with the MSI-high phenotype than in EGCs with the MSS phenotype. KRAS and BRAF mutations were rare in EGCs. Thus, the MSI phenotype in EGC is a major precursor lesion in gastric cancer and is characterized by distinct clinicopathological and molecular features.

SUBMITTER: Sugimoto R

PROVIDER: S-EPMC4738431 | biostudies-other | 2016 Apr

REPOSITORIES: biostudies-other

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Project description:Gastric cancer is a heterogenous disease with different phenotypes, genotypes, and clinical outcomes, including sensitivity to treatments and prognoses. Recent medical advances have enabled the classification of this heterogenous disease into several groups and the consequent analysis of their clinicopathological characteristics. Gastric cancer associated with Epstein-Barr virus (EBV) and microsatellite-unstable tumors are considered to be the two major subtypes as they are clearly defined by well-established methodologies, such as in situ hybridization and polymerase chain reaction-based analyses, respectively. However, discrepancies in the histological diagnosis of gastric neoplasms remain problematic, and international harmonization should be performed to improve our understanding of gastric carcinogenesis. We re-evaluated Japanese cases of early gastric cancer according to the current World Health Organization (WHO) criteria and classified them into genomic subtypes based on microsatellite instability (MSI) and EBV positivity to determine the initial genetic events in gastric carcinogenesis. A total of 113 Japanese early gastric cancers (including low- and high-grade dysplasias) treated with endoscopic resection over 5 years were archived in our hospital. A histological re-evaluation according to the WHO criteria revealed 54 adenocarcinomas, which were divided into 6 EBV-positive (11.1%), 7 MSI-high (MSI-H, 13.0%), and 41 microsatellite stable cases (75.9%). MSI-H adenocarcinoma was confirmed by an immunohistochemistry assay of mismatch repair proteins. Programmed death-ligand 1 immunostaining with two antibodies (E1L3N and SP263) was positive in tumor cells of one MSI-H adenocarcinoma case (1/7, 14.3%). The proportion of stained cells was higher with clone SP263 than with E1L3N. Histologically, EBV-positive carcinomas were poorly differentiated (83.8%), and MSI-H cancers were frequent in well to moderately differentiated adenocarcinoma (85.7%), indicating that the EBV-positive subtype presented with high-grade morphology even when an early lesion. Our study indicates that the WHO criteria are useful for subdividing Japanese early gastric cancers, and this subdivision may be useful for comparative analysis of precursor lesions and early carcinoma.

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Clinicopathological and molecular alterations in early gastric cancers with the microsatellite instability-high phenotype.

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