Colorectal carcinomas from Middle East. Molecular and tissue microarray analysis of genomic instability pathways.

Objective: To evaluate the overall incidence of microsatellite instability (MSI), hereditary non polyposis colorectal cancer, and tumor supressor gene (TP53) mutations in Saudi colorectal carcinomas.
Methods: We studied the MSI pathway in Saudi colorectal cancers (CRC) from 179 unselected patients using 2 methods: MSI by polymerase chain reaction, and immunohistochemistry detection of mutL homologs 1 and mutS homologs 2 proteins. The TP53 mutations were studied by sequencing exons 5, 6, 7, and 8.
Results: Of the 150 colorectal carcinomas analyzed for MSI, 16% of the tumors showed high level instability (MSI-H), 19.3% had low-level instability (MSI-L) and the remaining 64% tumors were stable. Survival of the MSI-H group was better as compared to the MSI-L or microsatellite stable group (p=0.0217). In the MSI-H group, 48% were familial MSI tumors, which could be attributable to the high incidence of consanguinity in the Saudi population. The TP53 mutations were found in 24% of the cases studied.
Conclusion: A high proportion of familial MSI cases and a lower incidence of TP53 mutations are some of the hallmarks of the Saudi colorectal carcinomas, which need to be explored further.