PD-L1 Expression in Gliomas: A Potential Immunotherapeutic Target in High-grade Tumours

Gliomas are the most common primary tumours of the central nervous system, with glioblastoma (grade 4 glioma) being the most malignant form. Despite standard therapy, patient survival remains poor. Immune checkpoint blockade targeting the PD-1/PD-L1 axis has shown promise in other cancers, but its role in gliomas remains under investigation. This study evaluates PD-L1 expression in gliomas and its correlation with tumour grade. A total of 50 histologically confirmed glioma cases were studied. Tumours were graded according to WHO 2021 CNS classification, and immunohistochemistry (IHC) was performed using antibodies for IDH, ATRX, TP53, Ki67, and PD-L1. PD-L1 expression was scored using an immunoreactivity scale, and its association with tumour grade was analysed using ordinal regression. A p-value < 0.05 was considered statistically significant. Among the 50 gliomas, the majority were astrocytoma, IDH-mutant (54%) followed by glioblastoma, IDH-wild type (26%). Most tumours were grade 4 (44%), grade 2 (34%), or grade 3 (18%). PD-L1 expression was detected exclusively in grade 4 tumours, with 6 of 22 (27.27%) cases showing positive expression. No expression was noted in grade 1-3 tumours. The association between PD-L1 expression and tumour grade was statistically significant (p=0.007). PD-L1 expression is limited to high-grade (grade 4) gliomas, suggesting a role in immune evasion. These findings support the potential utility of PD-L1 as a biomarker to identify glioma patients who may benefit from anti-PD-1/PD-L1 immunotherapy.