The Clinical Significance of Microsatellite Instability in Patients with Right-sided Colorectal Cancer.

Background/aims: Colorectal cancer (CRC) with microsatellite instability (MSI) has a better prognosis than CRC with microsatellite stable (MSS). Recent studies have reported biological differences according to tumor location in CRC. In this study, we investigated the clinical significance of MSI in patients with right-sided CRC.

Methods: The medical records of 1,009 CRC patients diagnosed at our institute between October 2004 and December 2016 with MSI test results were retrospectively reviewed. The long-term outcomes of CRC patients with MSI were assessed with respect to tumor location using Kaplan-Meier curves and Cox regression models.

Results: The median follow-up duration for all 1,009 study subjects was 25 months (interquartile range, 15-38). One hundred twenty-four of the study subjects had MSI (12.3%) and 250 had right-sided CRC (24.8%). The patients with MSI and right-sided CRC had better disease-free survival (DFS) than those with MSS as determined by the log-rank test (p=0.013), and this result was significant in females (p=0.035) but not in males with right-sided CRC. Multivariate Cox regression analysis showed MSS significantly predicted poor DFS in patients with right-sided CRC (hazard ratio 3.97, 95% CI 1.30-12.15, p=0.016) and in female patients (hazard ratio 4.69, 95% CI 1.03-21.36, p=0.045).

Conclusions: The study shows MSI is a useful predictor of DFS in patients with right-sided CRC, especially in female patients.