Clinicopathological features and microsatellite instability (MSI) in colorectal cancers from African Americans

Abstract

African Americans (AAs) have a 1.5 times higher risk of colorectal carcinoma (CRC) than Caucasians. Gene silencing through CpG island hypermethylation has been associated with the genesis or progression of microsatellite instability (MSI) largely due to 1 target for hypermethylation being the DNA mismatch repair gene hMLH1; there is anecdotal evidence of an increased incidence of MSI among AAs. P16 and hMLH1 can be inactivated by hypermethylation of their respective promoter regions, abrogating the ability to regulate cell proliferation and repair processes. We studied such methylation, as well as hMHS2 expression in colorectal cancers from AA patients to determine if MSI is associated with epigenetic silencing. Experiments were conducted on matched normal and colon cancer tissues from AA patients (n = 51). A total of 5 microsatellite markers (D2S123, D5S346, D17S250, BAT25 and BAT26) were used to evaluate MSI status. P16 and hMLH1 promoter methylation status was determined following bisulfite modification of DNA and using methylation specific PCR, while immunohistochemistry (IHC) was used to examine expression of hMLH1 and hMSH2. A total of 22 (43%) cancers demonstrated microsatellite instability‐high (MSI‐H), while 27 were microsatellite stable (MSS) and 2 were microsatellite instability‐low (MSH‐L). Most of the MSI‐H tumors were proximal, well differentiated and highly mucinous. Most patients in the MSI‐H group were females (68%). The p16 promoter was methylated in 19 of 47 (40%) tumors. A total of 7 of these CRCs demonstrated MSI‐H (33%). The hMLH1 promoter was methylated in 29 of 34 (85%) tumors, of which 13 CRCs demonstrated MSI‐H (87%). hMLH1 and hMSH2 staining was observed in 66% and 38% of MSI‐H tumors, respectively. Overall, the prevalence of MSI‐H colorectal tumor was 2‐3‐fold higher, while the defect in the percentage expression of mismatch repair (MMR) genes (hMLH1 and hMSH2) was similar in AA patients compared to the U.S. Caucasian population. Similar numbers of AA MSS tumors with p16 and hMLH1 methylation likely indicate hemimethylation of genes that might reflect environmental or genetic influences that might be more common in the AA population. © 2005 Wiley‐Liss, Inc.

Diet, Lifestyle, and Genomic Instability in the North Carolina Colon Cancer Study

“…This was somewhat surprising because the available evidence suggests that MSI may be more frequent among African Americans compared with Whites and the elevated risk of MSI tumors among African Americans has been postulated to be related to dietary differences (37). Possibly, the small number of MSI-H cases precluded our ability to detect statistically significant differences by race.…”

A Matched Case-Control Study Using the Propensity Score on Differences in the Characteristics of Colorectal Polyps between Younger and Older Koreans: Proximal Shift in the Distribution of Colorectal Polyps among Older Koreans

“…Histopathological and morphological differences have been reported between proximal and distal colon cancer. 17,18 Moreover, epidemiological studies have revealed that the clinical risk factors for cancer development are also different between proximal and distal colon cancer. 13,19 However, the reasons for these differences between left-and right-sided cancer remain unknown.…”

Colorectal Carcinoma in Malaysians: DNA Mismatch Repair Pattern in a Multiethnic Population

“…Various insertions or deletions of the microsatellites without effective repair result in a "mutator" phenotype with effect on legions of genes eg PTEN, BAX, EGFR, TGFβRII, that have critical functions in cell signalling, apoptosis and proliferation etc (Iacopetta et al, 2010). Based on the evidently different rates of CRC amongst our major ethnic groups and in the light of hitherto conflicting reports of possible MSI differences in CRC of various ethnic populations (Ashktorab et al, 2003;Vilkin et al, 2009;De JesusMonge et al, 2010;Sylvester et al, 2012) we initiated a study to determine the status of DNA mismatch repair in our CRC cases via immunohistochemical detection of the mismatch repair (MMR) gene products, MLH1, MSH2, MSH6 and PMS2, known to fairly reflect MSI status (Pinol et al, 2005;Niessen et al, 2006). Apart from attempting to determine whether MSI status, as represented by proficient or deficient MMR protein expression, differs between our major ethnic groups, we also attempted to correlate MMR status with age and gender of patients and location, grade, histological type and stage of the CRC.…”