Background: Glioma remains challenging due to high recurrence rates and resistance to treatment. Diagnosis and follow-up in resource-constrained regions often leads to significant patient attrition. Serum microRNA (miRNA) expression profiles, which have been shown to correlate with tissue expression profiles, are detectable in peripheral blood samples, providing a promising avenue for non-invasive and repeatable liquid biopsies. miR-21 shows promise in many populations; however, there is a dearth of data from our region. Methodology: We collected 90 tumor tissues, 42 pre- and post-operative serum samples from glioma patients, and included 10 normal tissue adjacent to the tumor (NATs) along with serum samples from 8 healthy individuals and analyzed for miR-21 expression through RT-qPCR. Shapiro Wilk test was applied to calculate data distribution, ANOVA, Fisher's exact and Wilcox test, along with pairwise Student's t-test, were applied to determine the differences in gene expression. The expression level of miR-21 was assessed for correlation with Kaplan-Meier survival curves and different molecular markers (IDH, Ki-67, ATRX and p53). The quantitative hazard ratio was determined using Cox regression analysis. Results: miR-21 expression in tissue increased with the median fold expression of 2.35 in grade 2, 7.49 in grade 3 and 26 in grade 4 for glioma patients. The expression level showed significant difference between control tissue and grade 4 patients along with significant inter-comparison between grade 1 and grade 4, as well as grade 2 and grade 4. A 30-fold elevated expression of miR-21 has been noticed in patients above 50 years of age. Similarly, in serum samples a significant decline in miR-21 expression was observed in post-operative samples as compared to pre-operative samples in grade 2 (11-fold), grade 3 15-fold) and grade 4 (13-fold). Furthermore, there was positive correlation of miR-21 expression with tumor volume. IDH-wildtype and high Ki-67 expression in gliomas showed significant upregulation of miR-21 compared to IDH-mutant and low Ki-67 respectively. Patients with low miR-21 expression had significantly longer overall survival (OS) than patients with high miR-21 expression. Quantitative hazard analysis indicates that patients in the high expression group have a 3.4 times higher risk of mortality (95% CI: 1.6- 7.1), in comparison to patients in the low expression group with AUC of 0.742 (all p <0.05). Conclusion: This study demonstrates the potential of microRNA 21 as a serum biomarker for early, cost-effective diagnosis of glioma. Furthermore, it may inform the development of targeted treatment strategies for various glioma grades, particularly in our population.
