Microsatellite instability is a favorable prognostic indicator in patients with colorectal cancer receiving chemotherapy

Background & Aims: Adjuvant 5-fluorouracil (5-FU)-based chemotherapy is standard treatment for stage C colorectal cancer (CRC). Approximately 12% of CRCs are characterized by microsatellite instability (MSI), a hallmark of a DNA mismatch repair defect, We investigated the safety of adjuvant 5-FU-based chemotherapy for MSI+ CRC and compared the prognosis of MSI+ and MSI- CRC patients receiving adjuvant therapy, Methods: Previously, a prospective series consisting of 1044 consecutive CRCs has been collected and the MSI status of each sample determined. Patients with stage C cancer who had received adjuvant chemotherapy(n = 95) were followed up for 7-63 months (median, 31 months) after surgery, Results: No unexpected or serious adverse effects were observed when 5-FU-based chemotherapy was used as adjuvant treatment for MSI+ CRC, Three-year recurrence-free survival was 90% and 43% in the MSI+ (n = 11) and MSI- (n = 84) groups, respectively (P = 0.020), Conclusions: Adjuvant 5-FU-based chemotherapy is feasible for both MSI+ and MSI- CRCs, and patients with MSI+ CRC who receive adjuvant therapy have an excellent prognosis.