Glioblastoma invariably recurs despite aggressive and multimodal first-line treatment and no standardized second-line therapy exists. We previously reported that treatment with the antiviral drug valganciclovir as an add-on to standard therapy significantly prolonged overall survival in 102 patients with newly diagnosed glioblastoma compared to contemporary controls. Here we present the results of retrospective survival analyses including patients with glioblastoma that initiated valganciclovir therapy after recurrence. Twenty-nine patients with recurrent glioblastoma received valganciclovir as an add-on to second-line therapy at Karolinska University Hospital. Contemporary controls were 109 patients with glioblastoma who received similar second-line therapy at our institution. We retrospectively analyzed survival data of these patients. Patients with recurrent glioblastoma who received valganciclovir had longer median overall survival after recurrence than controls (12.1 vs. 7.4 months, respectively, p = 0.0028). The drug was well tolerated. Both patients who underwent re-operation and patients that were not re-operated after recurrence benefitted significantly from valganciclovir therapy. Valganciclovir prolonged survival after recurrence both in patients with an unmethylated and methylated MGMT promoter gene. Valganciclovir was safe to use and prolonged median survival after recurrence for patients with recurrent glioblastoma, re-operated or not after recurrence, and with methylated or unmethylated MGMT promoter gene.

Glioblastoma is the most common and aggressive primary malignant brain tumour in adults, with limited treatment options despite years of research. Since the 2005 introduction of the current standard of care, hundreds of clinical trials have failed to deliver significant breakthroughs. In 2002, human cytomegalovirus (HCMV) was detected in 100% of glioblastoma tumours. Although its role in cancer remains debated, and HCMV is not classified as an oncovirus, numerous studies have reported high viral prevalence in glioblastoma. HCMV can induce all 10 ‘hallmarks of cancer’ and has been shown to modify both tumour cell behaviour and the microenvironment, which may enhance tumour growth and promote immune evasion. The association between HCMV and poor glioblastoma prognosis has generated increasing interest in targeting the virus therapeutically. Our clinical studies suggest that adding antiviral treatment to standard care may improve survival in both primary and recurrent glioblastoma. Moreover, an mRNA-based HCMV pp65 dendritic cell vaccine has shown preliminary indications of a potential survival benefit in early phase studies. Future research should prioritize clarifying HCMV’s role in glioblastoma and rigorously evaluating antiviral and immunotherapeutic strategies in randomized clinical trials. This article is part of the theme issue ‘The indirect effects of cytomegalovirus infection: mechanisms and consequences’.

Background: Emerging evidence suggests that antiviral treatment targeting human cytomegalovirus (HCMV) may improve outcomes in patients with glioblastoma (GBM). In this study, we analyzed serological data from the placebo-controlled VIGAS1 trial (Eudra number 2006-002022-29), which assessed the effect of valganciclovir (VGCV) on GBM progression in 42 patients, for impact of VGCV in preventing HCMV reactivation. Methods: VIGAS1 patients had undergone radical surgery and were randomized to receive either VGCV (n = 22) or placebo (n = 20) alongside standard radiochemotherapy. Blood was prospectively collected at baseline and 3-, 12- and 24-week follow-up visits. GBM cell lines and a cytomegalovirus-infected murine brain cancer model were used to validate the clinical findings. Results: Over the 24-week study period, we found that HCMV reactivation, as inferred from IgM seropositivity, occurred in 58.3% of patients in the placebo group, whereas this was completely prevented in the VGCV-treated group except for one patient with no treatment compliance (p = 0.0005). HCMV reactivation was linked to early recurrence. IgG-positive patients treated with VGCV showed a significantly longer time to progression (TTP) than those receiving placebo (6.7 vs. 3.7 months, p = 0.0408). We found a significant association between higher steroid doses and enhanced reactivation in the placebo group. In vitro and murine studies confirmed that corticosteroids, combined with radiation therapy, enhanced cytomegalovirus reactivation, which was mitigated by antiviral treatment. Conclusions: These findings suggest that preventing HCMV reactivation with antiviral therapy may improve patient outcomes, especially in HCMV-seropositive GBM patients, and further support the hypothesis that HCMV is a tumor-promoting virus.