Novel genetic and epigenetic alterations in ... - Ous-research.no

samples taken distant from MSI- and CIMP-positivetumors,[46] thus a higher degree of methylationmight be expected.A suitable, highly specific, biomarker should beunmethylated in normal mucosa from healthyindividuals and frequently methylated in carcinomas,and possibly also in benign lesions. To date, onlyfew such markers have been identified,[10,68,69]and one of the most suitable ones, Vimentin, is nonexpressedin a normal, healthy, colon.[69] The factthat an important biomarker is non-expressed innormal tissue supports the choice of a low thresholdfor methylation positive early lesions, applied in thepresent search for early onset biomarkers.Hypermethylation of genes such as ADAMTS1 andMAL are also suitable biomarkers for earlydetection, as they are infrequently methylated innormal mucosa taken from individuals withoutcancer (0% and 5%, respectively), but highlymethylated in malignant lesions (71% and 82%,respectively)[9,13]. In addition, both are frequentlyhypermethylated among the adenomas (37% and71%, respectively) independent of size. Of course,sufficient sensitivity and specificity of thesehypermethylation markers must be shown in fecesor blood samples for the purpose of non-invasivetesting. It should be note that this is an obstacle yetto be overcomed by suggested markers in existingnon-invasive tests.It has been speculated that methylation of specificgenes, such as MGMT, may yield a so-called “fieldeffect”, providing favorable conditions for furtheralterations which eventually might lead to tumorformation.[58,70] The initial steps in tumorigenesismight be due to an epigenetic disruption of aprogenitor/stem cell which may be followed bygenetic mutations of gatekeeper genes, and thesubsequent acquisition of other genetic andepigenetic alterations.[71] This model provides apossible explanation of why we see relatively highmethylation frequencies for genes such as MGMT,and HOXA9 in normal samples taken from cancerpatients.Summarized, this study has shown that genespecificpromoter hypermethylation is an early eventin colorectal tumorigenesis, exemplified byhypermethylation of MGMT in adenomas andnormal mucosa from cancer patients, and by thehigh frequency of ADAMTS1 and MAL methylationin polyps irrespective of size. These markers aresuitable as part of a panel aiming at detecting earlycolorectal lesions, and possibly a field effect in a“labile” colon. In general, we saw that aberrant CpGisland hypermethylation increased with malignancy.Finally, methylation of CRABP1, MLH1, NR3C1,RUNX3, and SCGB3A1 were identifiers of MSIcarcinomas.Competing InterestsThe author(s) declare that they have no competinginterests.Authors’ ContributionsAll authors have read and approved the final versionof the manuscript. TA was main responsible for thelaboratory analyses, performed statistical analyses,made all figures and drafted the manuscript. GELparticipated in the study design, in experimentalanalyses and in the preparation of the manuscript.VLC performed the quantitative methylation specificPCR analysis. GIM collected the cancer series andprovided the clinicopathological information. MVparticipated in the screening study from which wereceived adenomas and patient information. GSHwas responsible for the screening study from whichwe received adenomas and patient information.TOR collected and provided normal mucosa fromnon-cancerous individuals, the carcinoma seriesand participated in scientific discussions. RIScontributed to the statistical analyses and inscientific discussions. ETE participated in thescreening study from which we received adenomasand patient information as well as in study designand scientific discussions. RAL conceived the study,participated in the evaluation of the results and inmanuscript preparation.AcknowledgementsThis study was funded by grants from theNorwegian Research Council (163962/V50 and161448/V40, RAL), the latter supporting TA as aPhD student. Funding was also received from theNorwegian Cancer Society (A95068, RAL)supporting GEL as post doctoral fellow.References1. Ponz dL, Di Gregorio C: Pathology of colorectalcancer. Dig Liver Dis 2001, 33:372-388.2. Grady WM, Markowitz SD: Genetic and epigeneticalterations in colon cancer. 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