No Change in Frequency of Microsatellite Instability in Colorectal Cancers over a Period of 15 or More Years

Abstract

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.