Genetic differences stratified by PCR-based microsatellite analysis in gastric intramucosal neoplasia.

BACKGROUND: Although genetic alterations in patients with advanced gastric cancer have been extensively studied, those in patients with intramucosal neoplasia (IMN) are still poorly understood. METHODS: We evaluated genetic differences in 158 IMNs, including 51 low-grade dysplasias, 58 high-grade dysplasias (HGDs), 30 intramucosal cancers (IMCs), and 19 mixed tumors (composed of IMC and HGD within the same tumor), using PCR-based microsatellite analysis [allelic imbalance (AI) and microsatellite instability (MSI)]. We classified the DNA methylation status as a hypermethylated epigenome, a moderately methylated epigenome, or a hypomethylated epigenome. In addition, p53 overexpression, ß-catenin nuclear localization, and mucin expression were also examined. RESULTS: From cluster analysis, the IMNs examined were categorized into four subgroups as follows. Tumors in subgroup 1 were characterized by MSI-high status, a hypermethylated epigenome, and loss or reduction of expression of MLH-1. Tumors in subgroup 2 showed a mixed pattern consisting of AI and MSI. In contrast, tumors in subgroup 3, which showed accumulation of multiple AIs, were closely associated with HGD, IMC, or mixed tumor and exhibited nuclear expression of ß-catenin. Tumors in subgroup 4, which were generally low-grade dysplasias, exhibited a low frequency of AIs and no MSI. Although the mucin phenotype was not correlated with any subgroup, expression of mucin was associated with some subgroups. Overexpression of p53 was common in all subgroups. CONCLUSION: The approach described herein was useful for studying genetic differences in IMNs. In addition, we suggest that stratification of genetic differences may help to identify genetic molecular profiles in IMNs.

Analysis of molecular alterations in laterally spreading tumors of the colorectum.

BACKGROUND: Colorectal laterally spreading tumors (LSTs) are classified into LST-Gs and LST-NGs, according to macroscopic findings. In the present study, we determined the genetic and epigenetic alterations within colorectal LSTs and protruding adenomas. METHODS: A crypt isolation method was used to isolate DNA from tumors and normal glands of 73 macroscopically verified colorectal LSTs (histologically defined adenomas; 38 LST-Gs and 35 LST-NGs) and 36 protruding adenomas. The DNA was processed using polymerase chain reaction (PCR) microsatellite assays, single-strand conformation polymorphism (SSCP) assays, and pyrosequencing to detect chromosomal allelic imbalance (AI), mutations in APC, KRAS, and TP53, and the methylation of MLH1, MGMT, CDKN2A, HPP1, RASSF2A, SFRP1, DKK1, ZFP64, and SALL4 genes. In addition, methylation status was examined using the following set of markers: MIN1, MINT2, MINT31, MLH1, and CDKN2A (with classification of negative/low and high). Microsatellite instability (MSI) was also examined. RESULTS: 5q AI and methylation of the SFRP1 and SALL4 genes were common molecular events in both LST-Gs and LST-NGs. Neither MSI nor mutations in BRAF ware observed in the LSTs. TP53 mutations were rarely found in LSTs. The frequencies of KRAS and APC mutations and the methylation levels of ZFP64, RASSF2A, and HPP1 genes were significantly higher in LST-Gs than in LST-NGs. Protruding adenomas showed alterations common to LST-Gs. Negative/low methylation status was common among the three types of tumors. CONCLUSION: Combined genetic and epigenetic data suggested that the molecular mechanisms of tumorigenesis were different between LST-Gs and LST-NGs.