MICROSATELLITE INSTABILITY IN COLORECTAL-CANCER - IMPROVED ASSESSMENTUSING FLUORESCENT POLYMERASE CHAIN-REACTION

Background & Aims: Microsatellite instability was first described in h ereditary nonpolyposis colorectal cancers and sporadic colorectal canc ers, 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 d etecting microsatellite instability. Methods: Eleven fluorescently tag ged microsatellites and an automated DNA sequencer were used to invest igate 54 sporadic colorectal adenocarcinomas. Results: This fluorescen t assay combined accurate allele sizing with cross-sectional data disp lay and allowed improved assessment of microsatellite instability. Twe nty-two percent of cancers (12 of 54) showed microsatellite instabilit y with at least one marker. For tumors showing microsatellite instabil ity, results were obtained for a minimum of eight markers. Six tumors showed microsatellite instability at high frequency (at least 63% of m arkers affected), and 42% of the patients who had a tumor showing micr osatellite instability had a synchronous and/or metachronous colorecta l tumor (vs. 7% of patients whose tumor did not show microsatellite in stability). Patients with a microsatellite instability-positive tumor had an improved prognosis (P = 0.03). Conclusions: The use of this flu orescent assay improved the assessment of microsatellite instability w ith the automated analysis and cross-sectional data display. The assay identified a subgroup of patients who showed microsatellite instabili ty and who also showed clinical features that differed from the micros atellite instability-negative cases.