Predictors for High Microsatellite Instability in Patients with Colorectal Cancer Fulfilling the Revised Bethesda Guidelines

Background: The revised Bethesda guidelines (rBG) are generally used for screening of Lynch syndrome, and few researchers have investigated the associations between microsatellite instability (MSI) status and each item of the rBG. Patients and Methods: This retrospective study included patients with colorectal cancer who were classified into those fulfilling the rBG (Bethesda group) and those not (control group). The breakdown of each item in the rBG and predictors of high MSI (MSI-H) were determined in the Bethesda group. Results: Of 809 consecutive patients, 161 (19.9%) were found to fulfil the rBG criteria. As a predictor of MSI-H, items 2 or 5 of the rBG showed a sensitivity of 93.3%. Item 5 and right-sided tumour location were independent predictors of MSI-H in patients fulfilling the rBG (odds ratio(OR)=4.49 and 25.1; p=0.0260 and <0.0001, respectively). Conclusion: Item 5 of the rBG and right-sided tumour location are significant predictors of MSI-H.