Progressive methylation during the serrated neoplasia pathway of the colorectum

Abstract

Serrated adenoma is a recently described entity characterized by having combined architectural features of hyperplastic polyps and classical adenoma. To understand the role of gene regulation in the progression of the serrated neoplasia pathway, we examined the methylation profiles of the promoter regions of 19 genes, DNA ploidy, and mutator phenotype status. In all, 40 sporadic, classical serrated adenomas were pathologically reviewed and divided into four pathologic groups according to their histologic grades. Methylation-specific PCR was performed using primers for p16, hMLH1, RASSF1A, APC, HIC-1, DAPK, MGMT, SLC5A8, RB1, HCadherin, E-Cadherin, TIMP3, PTEN, THBS1, LKB1, p14, p15, FHIT, and VHL. Dual flow-cytometric analyses using cytokeratin and DAPI and MSI studies using BAT26 were also performed. Methylation was observed in 2.5-82.5% (mean 33.9%) of the CpG islands in the promoter regions of 16 genes. The tumors with higher histologic grades, including carcinomas, showed more extensive methylation compared to those with lower grades, and serrated adenomas in the right colon showed more frequent methylation than those in the left (Po0.05). Tumor-specific promoter methylation of SLC5A8 was observed in 33 (82.5%) of the serrated adenomas. Aneuploidization with near-diploid DNA indices was detected in four out of 28 cases examined (14.3%); two were low-grade serrated adenomas and two were carcinomas in the left colon. The high mutator phenotype was not observed in any of the cases examined. Our results indicate that: (1) aberrant, widespread methylation of CpG islands increases with the histological progression of serrated adenomas; (2) methylation of SLC5A8 is an early event; and (3) additional methylation of the p16, p14, MGMT, TIMP3, and FHIT genes are important tumorigenic steps in the serrated neoplasia pathway.

MLH1 promoter hypermethylation in the analytical algorithm of Lynch syndrome: a cost-effectiveness study

“…Interestingly, some evidence suggests that non-LS MSI-H cases may originate from sessile serrated adenoma. 41,42 In our case, no serrated phenotype was observed. The somatic profile of this tumor suggests that hypermethylation is the second inactivating hit.…”

CpG island methylator phenotype-low (CIMP-low) colorectal cancer shows not only few methylated CIMP-high-specific CpG islands, but also low-level methylation at individual loci

“…Transcriptional inactivation of tumor suppressor genes by promoter CpG island methylation is an important mechanism in human carcinogenesis. 2,[34][35][36][37][38] To measure the degree of DNA methylation, we used quantitative PCR assays (MethyLight), 20 which is essential to reproducibly differentiate low-level methylation from high-level methylation. 21,24 Our resource of a large number of samples of colorectal cancer (relatively unbiased samples compared to retrospective or single-hospital-based samples), derived from two large prospective cohorts, has enabled us to precisely estimate the frequency of low-level CpG island methylation in colorectal cancers at a population level.…”

Serrated polyps of the colorectum: is sessile serrated adenoma distinguishable from hyperplastic polyp in a daily practice?

“…Twenty-nine remaining polyps (28%) were serrated lesions but a more precise diagnosis could not be made on the first histologic review because the biopsy specimens were either small (all measured less than 5 mm) or superficial or tangentially oriented. Moreover, all of them were resected in multiple fragments (between [3][4][5], rendering the morphologic analysis more difficult. In these cases, the architectural features of either HP or SSA were difficult to be assessed.…”