Microsatellite instability (MSI) is a molecular
change resulting from inactivation of DNA mismatch repair systems, occurring
with a reported incidence between 15% - 20% of all sporadic colorectal cancers.
Our aim was to determine whether a change in the incidence of MSI in colorectal
cancer had occurred at our institution over time. We assayed 106 cases from the
mid-1990s and 69 cases from 15 or more years later for MSI. Those tumors with
MSI were assayed for BRAF mutation
and methylation. MSI was detected in 15 (14.2%) of the early cases and 11
(15.9%) of the later cases. For the two groups with MSI, a similar percentage
was methylated and had a BRAF mutation. One tumor in each group was MSI, unmethylated, and BRAF wild type. Our data indicate
consistency in the frequency of microsatellite unstable colorectal cancer
across a time span of 15 or more years.
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