The role of microsatellite instability to predict clinical benefit from irinotecan-based regimens in metastatic colorectal cancer

The aim of our study was to assess the relationship between microsatellite instability (MSI) and the clinical outcome in metastatic colorectal cancer (CRC) patients treated with irinotecan-based regimens. We assessed best objective response, progression free survival (PFS) and overall survival (OAS) in relation to MSI analysis that was performed using BAT-25, BAT-26, D5S346, D2S123, D17S250 markers in normal and tumor DNA. The best objective response was significantly and negatively related with the D17S250 (an adjacent locus to p53) microsatellite marker (p=0.047). However, MSI score was not related with the best objective response (p=0.88). There was again no relationship between PFS, OAS and MSI score. In conclusion, this study allowed us to establish in a prospective study design that MSI status did not predict survival in metastatic colorectal cancer patients treated with irinotecan-based regimens.