Microsatellite instability in colorectal cancer: improved assessment using fluorescent polymerase chain reaction

Microsatellite instability was first described in hereditary nonpolyposis colorectal cancers and sporadic colorectal cancers, in which it was associated with a good prognosis. The aim of this study was to assess the advantages of a novel fluorescent assay for detecting microsatellite instability.

Eleven fluorescently tagged microsatellites and an automated DNA sequencer were used to investigate 54 sporadic colorectal adenocarcinomas.

This fluorescent assay combined accurate allele sizing with cross-sectional data display and allowed improved assessment of microsatellite instability. Twenty-two percent of cancers (12 of 54) showed microsatellite instability with at least one marker. For tumors showing microsatellite instability, results were obtained for a minimum of eight markers. Six tumors showed microsatellite instability at high frequency (at least 63% of markers affected), and 42% of the patients who had a tumor showing microsatellite instability had a synchronous and/or metachronous colorectal tumor (vs. 7% of patients whose tumor did not show microsatellite instability). Patients with a microsatellite instability-positive tumor had an improved prognosis (P = 0.03).

The use of this fluorescent assay improved the assessment of microsatellite instability with the automated analysis and cross-sectional data display. The assay identified a subgroup of patients who showed microsatellite instability and who also showed clinical features that differed from the microsatellite instability-negative cases.