Prognostic Significance of Microsatellite Instability in Turkish Patients with Stage II and III Colorectal Cancer

Abstract

Objectives: Microsatellite instability (MSI) – a form of pervasive erratic expansion of microsatellites – can be identifiedin 15−20% of all patients with sporadic colorectal cancer (CRC). To gain further insight into the prognostic value of MSIin CRC, we sought to investigate this issue in a nonselected sample of Turkish patients seen in daily practice and toestablish whether the MSI status is associated with survival outcomes. We specifically focused on patients with stage 2and stage 3 CRC because they are a heterogeneous group in need of an improved clinical management.Methods: A total of 81 patients were enrolled into the study. MSI analysis was performed a dedicated platform andclassified into three types, as follows: microsatellite stability (MSS), low microsatellite instability (MSI-L), and high microsatellite instability (MSI-H). Disease-free survival (DFS) and overall survival (OS) served as the main outcome measures.Results: Patients with MSI-H had a significantly higher frequency of right colon tumors compared with those withMSI-L/MSS. Moreover, no cases of rectal tumor were observed in the former group (p=0.002). As a result, the use ofradiotherapy was limited to patients with MSI-L/MSS (p=0.02). Patients with MSI-H did not differ from those with MSI-L/MSS both in terms of DFS and OS.Conclusion: Our study demonstrates that Turkish patients with proximal colon cancer more frequently have MSI-Hcompared to those with distal colon cancer. However, the MSI status did not have a significant impact on survival outcomes.