Abstract BACKGROUND High-grade gliomas (HGGs) rapidly progress with a high recurrence rate and poor prognosis despite standard multimodal treatment. Valproic acid (VPA), a histone deacetylase inhibitor, sensitizes HGG to radiochemotherapy along with having potential anti-cancer mechanisms and augmenting the growth inhibitory effect of Temozolomide (TMZ). This study explores the effectiveness of VPA in combination with TMZ for treating patients with HGG. METHODS A comprehensive literature search was performed on PubMed, Scopus, Embase, and Web of Science databases and identified relevant studies (case-control, cohort, RCTs) comparing the synergistic effect of VPA during TMZ to TMZ without VPA. We investigated median overall survival (OS), Progression-free survival (PFS), and baseline MGMT methylation status to evaluate this relationship. RESULTS Our systematic review encompassed 9 studies involving 4,097 patients with HGGs (seven cohorts, one case-control, and one RCT). The pooled analysis of median OS demonstrated no statistical significance difference between VPA during TMZ and TMZ alone (MD=-3.97; 95%CI=-8.43-0.49; p=0.08). However, sub-analysis showed a statistically significant effect in studies with sample size <100 (MD=-5.06; 95%CI=-9.32,-0.80; p<0.02), and 100-200 (MD=-7.07; 95%CI=-13.15,-1.00; p<0.02), and those conducted before 2015 (MD=-5.62, 95%CI=-9.08,-2.17, p<0.01). On meta-regression analysis, no statistical significance (RC=0.82,95% CI=0.39,-2.03, p=0.18) was observed, indicating that the study year is not associated with the intervention. A separate analysis of 3 studies also showed no significant variance in the baseline percentage of patients without MGMT methylation (log OR=-0.35, 95%CI=-1.02,-0.32, p=0.30) when administering VPA during TMZ treatment (n=67) compared to TMZ alone (n=409). Additionally, VPA during TMZ does not significantly affect PFS (MD=-3.54; 95% CI=-10.18-3.10, p=0.30) compared to TMZ alone. CONCLUSIONS The concurrent use of VPA with TMZ shows no significant effect on OS and PFS, nor does it show any variance in the baseline MGMT methylation status compared to TMZ alone. However, smaller sample sizes show a significant effect. Thus, our findings emphasize the imperative for additional research aimed at refining clinical outcomes.
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