Microsatellite instability in sporadic colon cancer is associated with an improved prognosis at the population level

Some previous studies have reported an improved prognosis in sporadic colon cancers with microsatellite instability, whereas others have not. In addit ion, relatively few of those reporting an improved prognosis controlled for tumor stage or were population-based. Therefore, we evaluated the relation ship between microsatellite instability and prognosis, tumor stage, and oth er clinical variables in a population-based study of 1026 individuals. Micr osatellite instability was determined by the noncoding mononucleotide repea t BAT-26 and the coding mononucleotide repeat in transforming growth factor -beta receptor type II. Significant relationships were seen between microsa tellite instability and proximal tumor location, female gender, young and o ld age at diagnosis, poor histological differentiation, and low tumor stage (P < 0.01). There was a significant relationship between microsatellite in stability and improved prognosis, even after adjusting for stage, with a re duction in the risk of death attributable to colon cancer of <similar to>60 %. Most of this risk reduction occurred in individuals with American Joint Committee on Cancer stage III tumors, although transforming growth factor-b eta receptor type II mutations were associated with a significant reduction in colon cancer death in tumors with distant metastases. We conclude that microsatellite instability in sporadic colon cancer is associated with an i mproved prognosis at the population level.