Investigation of mismatch repair protein expression in glioma.

Mismatch repair (MMR) proteins are essential for maintaining genomic stability, and their dysfunction contributes to tumorigenesis in several malignancies. However, their role in glioma remains insufficiently defined. This study evaluated MMR protein expression in Tunisian glioma patients and examined its clinicopathological and prognostic significance. Ninety-five glioma samples were retrospectively analyzed. MMR protein expression was assessed by immunohistochemistry on formalin-fixed, paraffin-embedded tissues. Survival outcomes were evaluated using Kaplan-Meier analysis with Log-Rank testing. MMR expression was retained in 65 tumors (68.4 %) and lost in 30 (31.6 %). Loss of MLH1/PMS2 was observed in 16 tumors, MSH2/MSH6 loss in 12, and complete loss of all MMR proteins in two tumors. The distribution of MMR deficiency varied by histological subtype. Among pilocytic astrocytomas, 7 cases exhibited MMR deficiency, predominantly MLH1/PMS2 (n = 5). Two astrocytomas IDH mutant showed either MLH1/PMS2 or MSH2/MSH6 loss. Altered MMR profiles were also identified in oligodendroglioma IDH-mutant, 1p/19q co-deleted (n = 3), oligoastrocytoma NOS (n = 1), and anaplastic oligodendroglioma NOS (n = 1). In glioblastoma, IDH-wildtype, 14 cases showed heterodimer loss (MLH1/PMS2 or MSH2/MSH6), and two tumors demonstrated complete loss of all MMR proteins. Survival analysis revealed a significant prognostic effect exclusively in glioblastomas IDH-wildtype, where MMR deficiency was associated with worse survival (Log-rank test, p < 0.0001). MMR deficiency is relatively frequent in gliomas and carries prognostic significance, particularly in glioblastoma IDH-wildtype. Incorporating MMR status into molecular profiling may enhance risk stratification and inform therapeutic decision-making in glioma management.