A prospective analysis of microsatellite instability as a molecular marker in colorectal cancer

Background: Microsatellite instability (MSI) may be a molecular marker of colorectal tumor biology. We sought to evaluate the incidence and significance of MSI in an unselected colorectal cancer population. Methods: Colorectal cancer cases from a community health system were prospectively evaluated for MSI and patient outcomes monitored. Results: Of 240 eligible, 140 underwent testing; 43 (31%) had high-frequency MSI (NISI-H). Those with M[SI-H tumors presented with earlier disease stage (P = .014) and lymphocytic infiltration (P < .001). Stage III MSI-H patients trended toward improved disease-free survival (P = .065). MSI-H patients were more likely to have other primary malignancies. Conclusions: Prevalence of MSI-H in the general colorectal cancer population is higher than previously reported. MSI testing of colorectal cancers is useful as part of a molecular profile to stratify patients for prognosis, treatment, and further study. Patients with NISI-H tumors are more likely to have other primary malignancies, suggesting a role for heightened screening. (c) 2006 Excerpta Medica Inc. All rights reserved.