Microsatellite instability in aberrant crypt foci from patients without concurrent colon cancer

Abstract

Aberrant crypt foci (ACF) are microscopic surface abnormalities that are putative precursors to colorectal cancer (CRC). ACF exhibit similar histological and molecular abnormalities to adenomas and CRC and potentially represent useful biomarkers of cancer risk. Microsatellite instability (MSI) is one molecular abnormality identified in concurrent ACF from CRC patients that may indicate a risk for progression. To determine if MSI can be detected in ACF from cancer-free subjects, we examined 45 ACF from 20 subjects undergoing colonoscopies. The group included 12 patients at elevated risk for CRC based on family history of CRC or personal history of CRC or advanced adenoma and 8 patients with no known risk factors. ACF were identified using close-focus magnifying chromendoscopy and collected by biopsy in situ. Genomic DNA was prepared from ACF and adjacent normal colonic epithelium isolated by laser capture microdissection and analyzed for MSI. MSI was identified in at least one marker from 9 of 30 (30%) lesions from patients at elevated risk for CRC and in 2 of 15 (13%) lesions from average risk patients. Using methylation-specific PCR analysis, we also examined the ACF for promoter hypermethylation of the DNA repair genes hMLH1 and MGMT and found moderate changes (8/39 and 3/32, respectively). Although we found only a limited relationship between hMLH1 hypermethylation and MSI, all the lesions with MGMT hypermethylation displayed an MSI-low phenotype. These lesions may be precursors to MSI-low CRC, providing a potential early biomarker to assess the effects of cancer prevention strategies.

Mutations in BRAF and KRAS Differentially Distinguish Serrated versus Non-Serrated Hyperplastic Aberrant Crypt Foci in Humans

“…ACF were visualized and photographed using an Olympus close-focus colonoscope (XCF-Q160ALE; Olympus Corp., Center Valley, PA) that by employing a focal length of 2 to 100 mm permits high magnification (Â60) to be sustained over a longer visualizing distance. This allows for an increased ACF retrieval rate on biopsy (12,13).…”

“…Frozen serial sections of ACF were prepared at 5 to 7 Am thickness on glass slides. Laser capture microdissection was done on frozen sections using the Veritas microdissection instrument (Molecular Devices, Sunnyvale, CA) as described in our previous studies (12,13). Whenever possible, adjacent normal mucosal cells directly abutting the aberrant crypts were collected separately by laser capture.…”

Colorectal carcinogenesis: Road maps to cancer

“…In one study the rate of MSI-H was 89% in adenomas found within 5 cm of a cancer, and 77% of those located > 5 cm from cancer [50] . MSI, of at least one marker, can occasionally be found in ACF [51] , and MSI-L ACF are associated with methylation of MGMT [51] . This lends support to the concept introduced above, that sporadic MSI-L cancers associated with MGMT methylation may represent a unique entity characterized by a common cluster of molecular and pathological events, some of which can be identified even at the earliest stages of carcinogenesis.…”

Normal colorectal mucosa exhibits sex- and segment-specific susceptibility to DNA methylation at the hMLH1 and MGMT promoters

“…Given their indisputable relevance to colorectal carcinogenesis, aberrant promoter methylation involving the hMLH1 and MGMT genes might be expected to occur at an early stage in this process (Greenspan et al, 2007;Menigatti et al, 2007), before the gut mucosa exhibits gross changes. Systematic analysis of normal-appearing colorectal mucosa for cancer-relevant DNA methylation changes at these two gene promoters could thus provide insight into the pathological significance of similar changes found in colorectal cancers.…”