Histopathological and Immunohistochemical Evaluation of Programmed Cell Death Ligand 1 Expression in Diffuse Gliomas: Correlation with Tumor Grade, IDH Status, and Prognostic Implications

Diffuse gliomas, the most common primary brain tumors, exhibit diverse biological behaviors. Histopathological grading remains essential for classification, but molecular markers such as programmed cell death ligand 1 (PD-L1) offer insights into tumor biology. PD-L1 modulates immune evasion by tumors and correlates with aggressiveness and poor prognosis. The objective of the study was to evaluate PD-L1 expression across glioma grades, its association with isocitrate dehydrogenase (IDH) status, and its prognostic significance. A prospective observational study was conducted on 60 glioma cases over 18 months. Histopathological grading was performed using Haematoxylin and Eosin staining, and immunohistochemistry was used to assess IDH status and PD-L1 expression. PD-L1 expression was scored as 0, 1 + , 2 + , or 3+ based on tumor cell positivity. Correlations between PD-L1 scores, IDH status, World Health Organization grades, Glasgow Outcome Scale (GOS), and 6-month patient outcomes were analyzed. Statistical analysis was performed. Associations between PD-L1 expression and clinicopathological parameters were analyzed using the chi-square or Fisher's exact test. A p-value < 0.05 was considered statistically significant. Higher PD-L1 expression was significantly associated with advanced glioma grades (p = 0.0004) and IDH wild-type status (p = 0.036). Poorer outcomes, including recurrence, residual disease, and 6-month mortality, were observed in cases with higher PD-L1 scores. For PD-L1 score 3 + , recurrence was 66.66%, residual disease 100%, and 6-month mortality 83.33%. Higher PD-L1 levels also correlated with worse GOS scores (p < 0.0001). PD-L1 expression correlates with tumor grade, IDH status, and poor prognosis, highlighting its role as a prognostic marker and therapeutic target in gliomas. These findings advocate for integrating PD-L1 evaluation into diagnostic and treatment strategies, particularly for high-grade gliomas like glioblastoma.