Prognostic significance of microsatellite instability in sporadic colorectal cancer

Background and aims: Colorectal cancers exhibiting microsatellite instability (MSI) appear to have unique biological behavior. The influence of MSI on the prognosis of sporadic colorectal cancers is controversial and requires further investigation. The aim of this study was to analyze the association between MSI status and clinicopathological features and prognosis in sporadic colorectal cancer patients. Patients and methods: Of the 322 consecutive colorectal cancer patients operated upon at the Seoul National University Hospital between January and December 1998, we examined the clinicopathological features and prognosis of 248 patients with sporadic primary colorectal cancer. The MSI status of these 248 patients has been reported in a previous study. Of the 248 patients, 23 (9.3%) had MSI+ tumors. The patients' clinicopathological parameters were obtained from their medical records, and follow-up and survival data were obtained from medical records and phone calls. Results: MSI+ sporadic colorectal cancers were found predominantly in the proximal colon (p<0.001) and were associated with poor differentiation (p=0.030), a lower preoperative serum carcinoembryonic antigen (CEA) level (p=0.012), and less frequent systemic metastasis (p=0.034) than MSI- tumors. Low tumor grade (p=0.022), low tumor T-stage (p=0.002), no lymph node metastasis (p<0.001), no systemic metastasis (p<0.001), adjuvant chemotherapy (p<0.001) and MSI+ status (p=0.038) were independent favorable prognostic factors for survival in sporadic colorectal cancer patients. Conclusion: MSI status was an independent favorable prognostic factor for survival in sporadic primary colorectal cancer patients.