MSI-H Group Research Articles

MSI and epigenetic changes in colorectal cancers from African Americans

3570 Background: Microsatellite instability (MSI) is observed in sporadic Colorectal carcinoma (CRC) reflecting promoter hypermethylation of the DNA mismatch repair gene hMLH1. Additionally, p16 and hMLH1 can be inactivated by hypermethylation of its promoter region, which would abrogate its ability to regulate cell proliferation and the repair process. This study was setup to determine if MSI is common in colorectal cancers from AA patients and if MSI is associated simultaneously with p16 and hMLH1 gene silencing by methylation in the CRC from AA patients. Methods: Five microsatellite markers were used to evaluate (normal and colon cancer tissues from the same subjects, N=34) MSI status, p16 and hMLH1 promoter methylation status were determined following bisulfite modification of DNA and using methylation specific PCR, while immunohistochemistry was used to examine expression of hMLH1. Results: Twenty three cancers demonstrated MSI-H, two cancer demonstrated MSI-L and the remaining twenty six tumors were microsatellite stable (MSS). Most of the MSI-H tumors were proximal, well differentiated and highly mucinous. Most patients in the MSI-H group were females (70%) while most of the MSI-L group (100) was male. The p16 promoter was methylated in five of the 34 tumors (14%). Seventeen CRCs demonstrated MSI-H, three of which showed p16 promoter methylation (16%). Most of the tumors were hMLH1 methylated (70%). Tumors were mostly right handed. In total, 37% tumors (that were assayed by IHC) showed loss of staining for hMLH1 and most of them were MSI-H (57%). In addition, loss of MSH2 staining was observed in 43% of MSI-H. Conclusions: The incidence of MSI-H lesions was 2–3 fold higher (45%) in our study group compared to the data reported for the general population. This difference might reflect dietary differences or genetic polymorphisms that may be common in the AA population. Odds ratio analysis indicates that the chance of female patients having MSI-H was 2.3 times more than male patients (P< 0.03). The reason for this gender difference is unknown. No significant financial relationships to disclose.

MSI and epigenetic changes in colorectal cancers from African Americans

3570 Background: Microsatellite instability (MSI) is observed in sporadic Colorectal carcinoma (CRC) reflecting promoter hypermethylation of the DNA mismatch repair gene hMLH1. Additionally, p16 and hMLH1 can be inactivated by hypermethylation of its promoter region, which would abrogate its ability to regulate cell proliferation and the repair process. This study was setup to determine if MSI is common in colorectal cancers from AA patients and if MSI is associated simultaneously with p16 and hMLH1 gene silencing by methylation in the CRC from AA patients. Methods: Five microsatellite markers were used to evaluate (normal and colon cancer tissues from the same subjects, N=34) MSI status, p16 and hMLH1 promoter methylation status were determined following bisulfite modification of DNA and using methylation specific PCR, while immunohistochemistry was used to examine expression of hMLH1. Results: Twenty three cancers demonstrated MSI-H, two cancer demonstrated MSI-L and the remaining twenty six tumors were microsatellite stable (MSS). Most of the MSI-H tumors were proximal, well differentiated and highly mucinous. Most patients in the MSI-H group were females (70%) while most of the MSI-L group (100) was male. The p16 promoter was methylated in five of the 34 tumors (14%). Seventeen CRCs demonstrated MSI-H, three of which showed p16 promoter methylation (16%). Most of the tumors were hMLH1 methylated (70%). Tumors were mostly right handed. In total, 37% tumors (that were assayed by IHC) showed loss of staining for hMLH1 and most of them were MSI-H (57%). In addition, loss of MSH2 staining was observed in 43% of MSI-H. Conclusions: The incidence of MSI-H lesions was 2–3 fold higher (45%) in our study group compared to the data reported for the general population. This difference might reflect dietary differences or genetic polymorphisms that may be common in the AA population. Odds ratio analysis indicates that the chance of female patients having MSI-H was 2.3 times more than male patients (P< 0.03). The reason for this gender difference is unknown. No significant financial relationships to disclose.

APC and CTNNB1 Mutations in a Large Series of Sporadic Colorectal Carcinomas Stratified by the Microsatellite Instability Status

Background: Adenomatous polyposis coli (APC) and β -catenin (encoded by CTNNB1 ) are important components in the WNT signalling pathway, a pathway altered in nearly all colorectal tumours. Conflicting results are reported on whether APC mutations are less common in tumours with a high degree of microsatellite instability (MSI-H) than in microsatellite stable (MSS) ones, and whether mutations in the regulatory domain of CTNNB1 substitute for APC mutations in the MSI-H tumours. Methods: A consecutive series of 218 primary colorectal carcinomas, stratified by MSI status, were analysed for mutations in the APC gene (by the protein truncation test) and in the CTNNB1 gene (by single-strand conformation polymorphism). Results: APC mutations detected in 66% of the patients were significantly more frequent in the MSS and MSI-L (low) tumours than in the MSI-H tumour group ( P < 0.001). The MSI-H tumours tended to have more frameshift mutations than the MSS/MSI-L tumours. The majority of the APC mutations were located in the mutation cluster region (MCR). Patients that had lost all β -catenin binding sites of the APC gene showed a shorter survival time than patients who retained some or all of these binding sites ( P = 0.045). Two mutations were found in the CTNNB1 gene, but neither of them was located in the regulatory domain in exon 3. Conclusion: This study confirms that APC mutations are less frequent in MSI-H tumours than in MSS and MSI-L tumours. However, CTNNB1 mutations do not substitute for APC mutations in MSI-H tumours in these Norwegian patients.