In CRC, the methylation status of multiple promoters can be predicted through knowledge of BRAF and, to a lesser extent, KRAS activating mutations, indicating that these mutations are closely associated with different patterns of DNA hypermethylation. These changes may be important events in colorectal tumorigenesis.

Background-Colorectal cancers (CRCs) with the CpG island methylator phenotype (CIMP) often associate with epigenetic silencing of hMLH1 and an activating mutation in the BRAF gene. However, the current CIMP criteria are ambiguous, and often result in an underestimation of CIMP frequencies in CRCs. Since BRAF and KRAS belong to same signaling pathway, we hypothesized that not only mutations in BRAF, but mutant KRAS, may also associate with CIMP in CRC.

Methylation of the RASSF2 and SFRP2 promoters in fecal DNA is associated with the presence of gastrointestinal tumors relative to non-neoplastic conditions. Our novel fecal DNA methylation assay provides a possible means to noninvasively screen not only for colorectal tumors but also for gastric tumors.

O 6 -methylguanine-DNA methyltransferase (MGMT) is a DNA repair gene which is frequently methylated in colorectal cancer (CRC). However, it remains controversial whether methylation of specific CpG sequences within MGMT promoter leads to loss of its protein expression, and if MGMT methylation correlates with G to A transition mutations in KRAS. Two methylation sensitive regions (Mp and Eh region) of MGMT promoter were investigated in 593 specimens of colorectal tissue: 233 CRCs, 104 adenomatous polyps (AP), 220 normal colonic mucosa from CRC patients (N-C) and 36 normal colonic mucosa specimens obtained from subjects without colorectal neoplasia (N-N) by combined bisulfite restriction analysis (COBRA). The region-specific methylation data were compared to the MGMT protein expression, spectrum of KRAS mutations and other clinical features. Extensive (including both Mp and Eh) and partial (either Mp or Eh) MGMT methylation were found in 24.5% and 11.6% of CRCs, 3.8% and 27.9% of APs, 0.5% and 7.7% of C-Ns and 2.8% and 2.8% of N-Ns, respectively. Extensive methylation of MGMT promoter was primarily present in CRCs while partial methylation was common in APs. Extensive methylation of MGMT promoter was associated with loss/reduced protein expression (p < 0.0001), as well as with G to A mutations in KRAS (p 5 0.0017). We herein provide first evidence that extensive methylation of MGMT promoter region is essential for methylation-induced silencing of this gene. Our data suggest that MGMT methylation may evolve and spread throughout the promoter in a stepwise manner as the colonic epithelial cells progress through the classical-adenoma-cancer multistep cascade. ' 2008 Wiley-Liss, Inc.Key words: O 6 -methylguanine-DNA methyltransferase; KRAS mutations; promoter methylation; colorectal cancer; adenomatous polyps O 6 -methylguanine-DNA methyltransferase (MGMT) is a DNA repair gene which removes promutagenic O 6 -methylguanine (O 6 -MeG) residues from DNA and is considered an important predictive factors for chemoresistance in human cancers. [1][2][3][4][5] Loss of MGMT function permits the increased accumulation of O 6 -MeG in DNA, which promotes tumorigenesis through G:C to A:T transition mutations in growth regulating genes such as KRAS and p53. 6-9 Mutations in MGMT have rarely been found, and it has been suggested that MGMT inactivation is primarily manifested through hypermethylation-induced silencing of its promoter in human cancers, including those of the colon and rectum. 5,[9][10][11][12][13][14] However, the associations between MGMT methylation and G to A transition mutations has not been consistently reproduced in different studies. 15,16 Central to this controversy is the fact that there is a lack of clear understanding for precise relationships between methylation of specific MGMT promoter regions and its relationship with the loss of protein expression.It is becoming increasingly clear that the distribution of methylated cytosines in the CpG islands of promoters is not uniform, and the regions most importan...

Background: Oesophageal squamous cell carcinoma (OSCC) often arises from preceding dysplastic lesions in the oesophageal epithelium. However, the molecular changes occurring in premalignant lesions are not well understood. An epigenetic change is an example of OSCC that may occur within the epithelium. Aim: To investigate the methylation status of multiple promoters in cancer-derived DNA, as well as in the background epithelium of OSCC, including dysplastic lesions and non-neoplastic mucosa. The normal epithelium from patients without cancer was also examined. The findings were correlated with the mutational status of p53. Patients and methods: 56 patients with advanced OSCC, 21 patients with intraepithelial neoplasia (IEN), 56 patients with a background of non-neoplastic epithelium, adjacent to the OSCC, and 42 normal control epithelia from healthy volunteers were studied. The promoter methylation status of SFRP1, SFRP2, DCC, APC, p16 INK4a , p14 ARF , MINT1, MINT2, MINT31, CACNA1G, COX2, DAPK, hMLH1 and MGMT was examined by methylation-specific single polymerase chain reaction or combined bisulphite restriction analysis. The mutation of p53 by direct sequencing was assessed. Results: DNA methylation was observed in OSCC and in its background epithelium. The frequency of CpG island methylation increased from a baseline level in the background non-neoplastic epithelium, through IEN, to advanced OSCC. However, mutations in p53 were almost exclusively observed in IEN and OSCC. More extensive DNA methylation was seen in the neoplastic lesions (OSCC or IEN) having a p53 mutation than in those with wild-type p53. Conclusion: DNA methylation is present at low levels in the non-neoplastic oesophageal epithelium and appears to contribute to the progression of the dysplasia-carcinoma sequence in OSCC carcinogenesis. D espite the increased incidence of oesophageal adenocarcinoma in the Western World, oesophageal squamous cell carcinoma (OSCC) remains a common type of malignancy worldwide. Tumorigenesis of OSCC is a multistep process and OSCC often develops multifocally within the oesophageal epithelium. Environmental and dietary factors, such as alcohol, tobacco, and high levels of nitrates in the soil and drinking water, have been associated with the aetiology of OSCC. Mutations in the p53 gene are one of the most frequent genetic changes observed in oesophageal cancer and dysplasia.3-5 A varying p53 mutational status is often observed in multiple lesions from the same patient with OSCC.6 Wide areas within the oesophageal mucosa become simultaneously genetically unstable after a prolonged exposure to carcinogens, leading to a pattern of neoplastic transformation described as ''field carcinogenesis''. [7][8][9] Epigenetic changes in DNA without concomitant changes in the underlying genetic code are now known to occur often in human cancers. [10][11][12] Promoter hypermethylation and resulting transcriptional repression of functionally important cancerrelated tumour suppressor genes appear to drive tumorigenesis. The prom...