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 (MSI-H). Those with MSI-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 MSI-H tumors are more likely to have other primary malignancies, suggesting a role for heightened screening.