Prognostic impact of microsatellite instability in colorectal cancer patients treated with adjuvant FOLFOX.

BACKGROUND Colorectal cancer (CRC) patients whose tumours have microsatellite instability (MSI) do not benefit from adjuvant 5-fluorouracil. However, the predictive value of MSI is not known for FOLFOX, now recommended in adjuvant setting. PATIENTS AND METHODS MSI phenotype was assessed by the pentaplex method. Three-year relapse and disease-free survival (DFS) of patients treated for CRC with FOLFOX 4 in an adjuvant setting were compared according to MSI phenotype. RESULTS A total of 105 patients (19 MSI, 86 microsatellite stable, MSS) were included. Stage II patients more frequently exhibited MSI (58%) than MSS (21%); (p=0.002). Patients with MSI relapsed significantly less than those with MSS (10.5% vs. 35.0%; p=0.04). DFS was similar for MSI and MSS (p=0.1). In univariate analysis, stage (p=0.0006) and MSI status (p=0.017) were significant predictors of DFS. CONCLUSION MSI status was associated with significantly fewer relapses and a better prognosis. FOLFOX4 did not alter survival of patients with MSI and can be administered to them.