DNA methylation patterns in adenomas from FAP, multiple adenoma and sporadic colorectal carcinoma patients

Colorectal adenomas have traditionally been regarded as homogeneous. The aim of our study was to identify molecular features that may differentiate sporadic adenomas from familial adenomas such as Familial Adenomatous Polyposis (FAP) and Multiple Adenoma patients. DNA methylation was tested at Methylated IN Tumor (MINT) loci (1,2,12,31) and the CpG promoter region of genes MLH1, HPP1, MGMT, p14ARF and p16INK4a in FAP-associated adenomas (33) from 5 patients with a known APC mutation (Group 1, FAP), adenomas (29) from 4 Multiple Adenoma patients (Group 2 Multiple), adenomas (14) from 3 patients with sporadic colorectal cancers showing high microsatellite instability (Group 3, MSI-H) and adenomas (16) from 7 patients, with sporadic colorectal cancers showing microsatellite stable or low level instability (Group 4, MSS/MSI-L). Aberrant Crypt Foci (ACFs), Hyperplastic Polyps (HPs) and cancers were also examined for methylation status as well as K-ras mutation. Multiple Adenoma patients were examined for germline polymorphisms in the base excision repair gene, MYH. The familial syndrome, FAP -associated adenomas showed a significantly low frequency of MINT methylation (15.5%,) compared to sporadic MSS/MSI-L-associated adenomas (35.5%). Group 3 (MSI-H) adenomas were different in that many showed serration and a high level of methylation (57.1%). Group 2, Multiple Adenoma cases, resembled sporadic MSS/MSI-L-associated adenomas. However the promoter regions of key genes, MGMT, p14ARF and p16INK4a were methylated to a greater extent than MINTs in both sporadic and familial adenomas. Genetic profiling of adenomas supports the concept that adenomas belonging to familial syndromes pursue a different pathway to tumorigenesis than their sporadic counterpar/ts from their earliest formation.