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Introduction Colorectal cancer (CRC) can arise through two distinct mutational pathways: microsatellite instability or chromosomal instability. High-frequency microsatellite instability (MSI) occurs in approximately 15 percent of sporadic cases of CRCs. Many studies have well established that MSI, the hallmark of defective DNA mismatch repair, is associated with prolonged survival of CRC patients compared with tumors that are microsatellite stable. CRCs in patients under 50 years of age are rare and represent about 5% of the total number of tumors. The aim of this study was to analyze the prognostic significance of MSI in CRC patients younger than 50 at the time of diagnosis. Matherial and methods 31 patients with CRC under 50 years of age were tested for the presence of MSI, and compared with 35 patients aged 50 or more at the time of diagnosis. CRC-specific survival five-year- follow-up period was analyzed in relation to MSI status. Results The frequency of MSI among the young patients was 35.48%, which was significantly higher than the rate of 11.43% noted in older patients with CRCs (p<0.042). This study revealed no difference in survival in patients with CRCs aged less than 50 compared with those over 50 years of age. The five-years survival of young CRCs patients with MSI 81.82%, was better than that of the patients with cancers with microsatellite stability, 60%, but there was no significant difference in statistics. Discussion and conclusion In our study there was no statistically detectable significant difference between tumor microsatellite status and survival in young patients, although we confirmed the previous observations that MSI is associated with better prognosis. We found that the pathological stage of CRC was an independent and powerful predictor of the clinical outcome. [ABSTRACT FROM AUTHOR]