Microsatellite Instability in Glioblastoma: Is It Really Relevant in Tumor Prognosis?

To evaluate the frequency and prognostic significance of microsatellite instability (MSI) in patients with glioblastoma (GBM), an immunohistochemical analysis of mismatch repair (MMR) proteins was performed. A total of 71 patients with GBM who underwent surgery between 2011 and 2019, were included in the study. MMR protein expression was examined using immunohistochemistical analysis of tumor tissue samples; the association between the MMR status and clinicopathological findings was evaluated. Immunohistochemical analysis revealed expressions of MLH1, MSH2, MSH6, and PMS2 proteins in 67 (94.4%), 65 (91.5%), 67 (94.4%), and 64 (90.1%) patients, respectively. Among the 71 patients, 64 (90.1%) expressing all MMR proteins were considered microsatellite stable (MSS), and 7 (9.9%) patients showing loss of at least one of the MMR proteins were considered to show MSI. Tumor recurrence was noted in 25 (39.1%) patients in the MSS GBM group, and 4 (57.1%) patients in the MSI GBM group (p=0.433). The overall median survival was 30.65 ± 5.1 and 10.71 ± 5.2 months in the MSS GBM and MSI GBM groups, respectively (p=0.059). The results of this study showed no significant relationships between MMR protein expression and recurrence rates or overall survival in patients with GBM.