miR-21 as a Diagnostic and Prognostic Biomarker in Glioma: Tissue and Serum Expression Analysis in a Pakistani Cohort

Background Gliomas are heterogeneous primary brain tumors with a poor prognosis, particularly in higher grades. MicroRNA-21 (miR-21) has emerged as a potential oncogenic biomarker in various cancers, including gliomas; however, its clinical utility in low- and middle-income countries (LMICs) remains underexplored. This study investigates the prognostic and diagnostic potential of miR-21 in glioma tissues and serum, examining its association with clinical and molecular features, tumor volume, and patient survival. Methodology We collected 90 tumor tissue samples, 42 paired pre- and post-operative serum samples from glioma patients, and 10 normal adjacent brain tissue (NAT) samples, along with serum samples from 8 healthy individuals, to assess miR-21 expression using RT-qPCR. The Shapiro-Wilk test was performed to evaluate the data distribution. To analyze differences in gene expression, we applied ANOVA, Fisher’s exact test, the Wilcoxon test, and pairwise Student’s t-tests. miR-21 expression levels were further examined for correlation with Kaplan-Meier survival curves and the status of molecular markers, including IDH, Ki-67, ATRX, and p53. The hazard ratio for miR-21 as a prognostic indicator was quantified using Cox regression analysis. Results MicroRNA-21 expression in glioma tissue progressively increased with tumor grade when compared to controls and across different glioma grades. A significant elevation in miR-21 expression was observed between grade 4 glioma tissues and control tissues, with additional significant differences between grade 1 and grade 4, as well as between grade 2 and grade 4. While tissue expression of miR-21 showed a positive trend with tumor volume, this correlation did not reach statistical significance. Moreover, gliomas with IDH-wildtype status and high Ki-67 expression demonstrated significantly higher miR-21 levels compared to IDH-mutant and low Ki-67 groups, respectively. Patients with low miR-21 expression had significantly longer overall survival (OS) compared to those with high miR-21 expression levels. Quantitative hazard analysis revealed that patients in the high-expression group had a 3.4-fold increased risk of mortality (95% CI: 1.6–7.1), with an AUC of 0.742 (all p < 0.05). Notably, significantly elevated miR-21 expression was found in patients over the age of 50. In serum samples, miR-21 expression was significantly lower in the healthy control group and in post-operative samples compared to pre-operative samples across grades 2, 3, and 4 glioma patients. This suggests its potential utility as a non-invasive diagnostic and monitoring biomarker. The decline in serum miR-21 levels following tumor resection supports its association with tumor presence and progression. However, the prognostic significance was limited by cohort size and grade imbalance. Conclusion miR-21 is significantly upregulated in both glioma tissue and serum, particularly in high-grade and IDH-wildtype tumors. It is strongly associated with poor clinical outcomes and aggressive molecular features. Its prognostic value is robust both alone and in combination with established markers. Furthermore, dynamic changes in serum miR-21 levels post-surgery highlight its potential utility in disease monitoring. These findings support the incorporation of miR-21 into glioma diagnostic and prognostic frameworks, enhancing clinical decision-making and personalized treatment approaches. miR-21 serves as a strong tissue-based prognostic marker in gliomas and a promising serum biomarker for tumor monitoring. While tissue findings align with global data, further studies are required to validate the serum results. This work underscores the clinical relevance of miR-21 in low- and middle-income countries (LMICs), where non-invasive tools are urgently needed.