Abstract
Microsatellite Instability (MSI) is a hallmark of colorectal cancer (CRC) and occurs in 15–16% of CRC. Molecular biological information of CRC in South Africa (SA) is largely unrecorded. This study was undertaken to determine the frequency of MSI, with particular reference to Lynch syndrome (LS) with a view to improve surveillance and prevention strategies. This was a retrospective study on CRC samples diagnosed between 2011–2015 at Charlotte Maxeke Johannesburg Academic Hospital (CMJAH). Samples diagnosed between 2011–2012 were screened for MSI by PCR and mismatch repair (MMR) immunohistochemistry (IHC), and additional BRAFV600E mutational analysis performed. T-tests, Fischer’s exact and Chi square statistical tests were applied. Twelve percent of patients displayed MSI, with increased frequency in black (15%) versus other ethnic group (OEG) (8%) patients. MSI patients were significantly younger than microsatellite stable (MSS) patients, however when stratified by ethnicity, black patients were predominantly younger (median age: 47), with increased MSH2/6 loss, and no BRAF mutations. These findings suggest a large proportion of young black SA CRC patients develop via the LS pathway due to earlier age onset and predominant MSH2/6 protein loss. SA patients of other ethnicities appear to follow the more well established sporadic MSI pathway.
Highlights
Colorectal cancer (CRC) develops through three major molecular pathways namely: Chromosomal Instability (CIN), Microsatellite Instability (MSI), and the epigenetic instability or CpG island methylator phenotype (CIMP) pathway[1,2,3]
A total 439 of 672 colorectal cancer (CRC) patients diagnosed between January 2011-December 2015 had MSI CRC status assessment
Black patients contributed to 60% (262/439) of cases. (Column[1] of Table 1)
Summary
Colorectal cancer (CRC) develops through three major molecular pathways namely: Chromosomal Instability (CIN), Microsatellite Instability (MSI), and the epigenetic instability or CpG island methylator phenotype (CIMP) pathway[1,2,3]. Previous CRC studies conducted in SA showed a higher frequency of MSI CRC in young black patients through MMR deficiency than white patients[21,22,23]. This study assesses the frequency and features associated with MSI CRC over a 5-year period in a cohort of newly diagnosed CRC patients at the Charlotte Maxeke Johannesburg Academic Hospital (CMJAH) within SA. This data will provide insight into the CRC histopathological and molecular features associated with MSI CRC in black SA patients, with particular reference to MSI CRC frequency and the occurrence of suspected LS, a heretofore largely unassessed aspect of the disease
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