The biology behind the measurement is central to why this matters. MGMT encodes O6-methylguanine–DNA methyltransferase, a repair enzyme that directly reverses the kind of DNA damage temozolomide inflicts. When the gene’s promoter is silenced by methylation — the addition of methyl groups to CpG dinucleotides in the regulatory region — tumor cells produce little of the repair protein and remain vulnerable to the drug. Methylation of the promoter is therefore a predictive biomarker: patients whose tumors are hypermethylated derive greater benefit from temozolomide, showing improved progression-free and overall survival, while those with unmethylated tumors respond poorly. In the study’s large molecular cohort, tumors classified as hypermethylated at the first time point carried a mean methylation percentage of 35.6 percent, ranging up to 89 percent, whereas unmethylated tumors averaged just 2.1 percent — a wide biological gulf that the binary labels tend to conceal.

To interrogate how that gulf behaves over the course of disease, the researchers, led by Henry Noren and Morana Vojnic of Rutgers Cancer Institute and collaborating institutions, turned to a large commercial molecular profiling database maintained by Caris Life Sciences. They identified patients with recurrent glioma who had undergone molecular testing at two distinct time points and, after excluding cases with insufficient tissue, assembled 426 paired samples. MGMT promoter methylation was assessed by pyrosequencing of CpG sites 74 through 78, following bisulfite conversion of DNA extracted from formalin-fixed paraffin-embedded tissue with at least 50 percent tumor nuclei. The laboratory reported both a quantitative methylation percentage and a categorical status: hypermethylated at 9 percent or above, equivocal between 7 and under 9 percent, and unmethylated below 7 percent. Equivocal cases were assigned to the unmethylated group for analysis, in line with prior studies.

The headline finding is strikingly simple. In 84 percent of tumors — 358 of 426 — the categorical MGMT status was identical at diagnosis and at recurrence, with 52 percent remaining unmethylated and 32 percent remaining hypermethylated. Only 16 percent changed status, and the direction of change was uneven: 11 percent shifted from hypermethylated to unmethylated, while just 5 percent gained hypermethylation. More importantly, when the researchers examined the underlying quantitative values, the average change in methylation percentage across the whole cohort was a modest minus 1.4 percentage points, with a standard deviation of 16.0. Tumors that kept their original classification barely moved at all, drifting by only minus 0.3 points in the consistently unmethylated group and plus 0.6 points in the consistently hypermethylated group. The epigenetic landscape, in other words, is largely frozen between the two surgeries.

The apparent transitions told a different and more instructive story. Tumors that flipped from hypermethylated to unmethylated had baseline methylation levels on average 13.5 percentage points lower than tumors that stayed hypermethylated, a difference that was highly statistically significant. Tumors that gained hypermethylation at recurrence had recurrence values on average 16.3 points lower than consistently hypermethylated tumors. In plain terms, the tumors that changed categories were clustered near the classification thresholds, where a small quantitative shift — whether from intratumoral heterogeneity, differences in sampling, assay variability, or modest epigenetic drift — is enough to move a tumor across the line. The authors conclude that most categorical status changes reflect variability at the margins of classification rather than true epigenetic reprogramming under therapeutic pressure, a distinction with real consequences for how clinicians should read a changed report.

The study also mapped methylation dynamics onto the temporal arc of the disease, using the interval between the two tissue collections as a surrogate for disease course. Among patients whose samples were collected at least three months apart, tumors that remained hypermethylated, lost hypermethylation, or gained hypermethylation all showed longer intervals between samples than tumors that stayed unmethylated. Consistently hypermethylated tumors had intervals 6.7 months longer than consistently unmethylated ones, and tumors that gained hypermethylation showed an 8.2-month difference, with both comparisons reaching statistical significance. The researchers interpret this descriptively: it mirrors the established association between MGMT hypermethylation and better response to alkylating chemotherapy, rather than implying that methylation changes themselves alter the disease trajectory. An exploratory geographic analysis added a curious footnote — frontal lobe tumors were more likely to remain hypermethylated at recurrence, at 41 percent, and less likely to remain unmethylated, at 45 percent, compared with tumors elsewhere in the brain.

To connect the molecular findings to actual clinical behavior, the team analyzed a separate retrospective cohort of 27 adult patients from two academic institutions, Rutgers Cancer Institute and Lenox Hill Hospital, with detailed treatment records. These patients were predominantly diagnosed with glioblastoma, which accounted for 74.1 percent of cases, and nearly all — 96.3 percent — received temozolomide after their initial surgery regardless of MGMT status, consistent with standard of care. At recurrence, 44.4 percent of the cohort was re-treated with the drug. The pattern of who got re-treated tracked the biomarker: temozolomide rechallenge was pursued in 54.5 percent of patients whose tumors remained hypermethylated, compared with 41.7 percent of those whose tumors stayed unmethylated, though the difference did not reach statistical significance in this small sample. Re-irradiation showed the inverse pattern, being more common among patients with consistently unmethylated tumors.

That treatment asymmetry echoes findings from larger clinical trials, including the DIRECTOR trial, which demonstrated that MGMT promoter methylation is a strong predictor of benefit from dose-intensified temozolomide rechallenge in progressive glioblastoma. Retrospective analyses have likewise shown that patients with retained hypermethylation gain more from a second course of the drug, while those with unmethylated tumors are more often directed toward alternative systemic therapies, clinical trials, re-irradiation, or supportive care. What the new study adds is real-world evidence that clinicians are, in fact, weighing MGMT status at recurrence when making these calls — and a quantitative argument that the status they weigh is usually the same one measured months or years earlier at diagnosis.

The implications for laboratory practice may prove to be the study’s most durable contribution. Because binary classification remains the norm in clinical reporting, tumors with borderline methylation — those hovering near the 7 and 9 percent cutoffs — can be labeled in ways that obscure their true position on what is increasingly understood as a quantitative continuum. Prior work has shown that intermediate or low-level methylation is associated with less predictable response to temozolomide and diminished prognostic value compared with clearly unmethylated or robustly hypermethylated tumors. The new data suggest these borderline tumors form a biologically less stable subgroup, vulnerable to reclassification between surgeries for reasons that may have little to do with genuine epigenetic evolution. Routine quantitative reporting, the authors argue, would give oncologists the context needed to interpret a changed status appropriately — and to recognize when a change is more artifact than biology.

The authors are careful to acknowledge the limits of their analysis. Both cohorts were retrospective, introducing potential selection and sampling biases; the interval between surgeries is an imperfect proxy for progression-free survival; the commercial database lacked treatment details, precluding adjustment for therapy-related confounders; and the 27-patient clinical cohort was too small and underpowered for survival analyses, making its findings exploratory. The molecular data also cannot fully disentangle the contributions of intratumoral heterogeneity, sampling variability, and selective pressure from chemotherapy. Still, with one of the largest paired cohorts of recurrent glioma assembled to date and the integration of quantitative methylation percentages alongside categorical labels, the study makes a compelling case that MGMT assessment at diagnosis remains clinically reliable — and that reassessing it at recurrence, with numbers rather than just labels, could sharpen one of the most difficult decisions in brain tumor medicine.

Subject of Research: Stability of MGMT promoter methylation in recurrent glioma and its implications for temozolomide rechallenge

Article Title: Quantitative stability of MGMT promoter methylation in recurrent glioma and implications for temozolomide rechallenge

Article References: Noren, H., Pelofsky, G., Suffren, B., Mittelman, L., Yohn, C., Twyman, A., Febres-Aldana, C. A., Abramyan, A., Sertil, A., D’Amico, R. S., Sherman, J. H., & Vojnic, M. (2026). Quantitative stability of MGMT promoter methylation in recurrent glioma and implications for temozolomide rechallenge. Journal of Neuro-Oncology, 179(3), Article 85. https://doi.org/10.1007/s11060-026-05778-y

Image Credits: AI Generated

DOI: 10.1007/s11060-026-05778-y

Keywords: glioma, glioblastoma, MGMT promoter methylation, temozolomide, epigenetics, DNA methylation, biomarker, pyrosequencing, recurrent brain tumor, chemotherapy rechallenge, precision oncology, neuro-oncology

The rationale behind the approach rests on a striking biological quirk. Although prostate-specific membrane antigen, or PSMA, takes its name from the prostate, it is also expressed on the neovasculature of many solid tumors, including glioblastoma. The rapidly growing blood vessels that feed these tumors display the protein at high density, while normal brain vasculature largely does not. This creates a therapeutic window: a radioligand that homes in on PSMA can deliver cytotoxic radiation to the tumor’s own blood supply, starving it from within while sparing healthy tissue. Previous work by Wernicke and colleagues established PSMA as a vascular target in glioblastoma, and multicenter imaging studies have since confirmed that PSMA-targeted PET tracers accumulate in a substantial proportion of high-grade gliomas, making the antigen both an imaging biomarker and a candidate therapeutic target.

Actinium-225 is among the most potent radionuclides available to nuclear medicine. It decays through a cascade of four alpha emissions, each depositing enormous energy over distances of only a few cell diameters. This dense, short-range radiation causes clusters of irreparable double-strand DNA breaks, killing targeted cells and even neighboring tumor cells through a bystander effect, regardless of oxygenation or cell-cycle status, factors that often blunt the effectiveness of conventional photon radiotherapy. The same short particle range, however, demands that the radionuclide be delivered with precision, which is precisely what the PSMA-targeting ligand is designed to achieve. In prostate cancer, [²²⁵Ac]-PSMA-617 has produced dramatic responses, but extending this technology to brain tumors required evidence that the ligand would actually localize to glioma tissue in patients.

To test the concept, the researchers treated four patients with histologically confirmed recurrent high-grade glioma: three with glioblastoma and one with a WHO grade III high-grade diffuse glial tumor. Each patient received [²²⁵Ac]-PSMA intravenously at a dose of 100 kilobecquerels per kilogram of body weight per cycle, with treatment cycles intended at intervals of eight to twelve weeks. Before therapy, all patients underwent PSMA-targeted PET imaging with either [⁶⁸Ga]-PSMA PET/MRI or PET/CT, combined with contrast-enhanced magnetic resonance imaging, to identify PSMA-avid index lesions. Baseline and follow-up assessments were performed visually and then quantified using semi-quantitative parameters on the hybrid imaging studies, while clinical status and hematologic parameters were monitored throughout therapy and follow-up.

The imaging results offered cautious grounds for optimism. Although every patient ultimately developed progressive disease, the predefined PSMA-avid index lesion regressed in one patient and remained stable in another. In a disease where progression is typically rapid and relentless, any evidence of local disease control is noteworthy, particularly with a first-in-kind systemic therapy delivered on an outpatient basis. The investigators emphasize that the study was designed to assess feasibility, safety, and preliminary efficacy rather than survival outcomes, and the small cohort of four patients means that no firm conclusions about efficacy can yet be drawn. Nevertheless, the observation that a radiopharmaceutical could produce measurable tumor control in heavily pretreated brain tumor patients represents a proof of principle for the entire strategy.

Safety findings were equally encouraging. No grade three or higher adverse events attributable to [²²⁵Ac]-PSMA were observed, and there were no treatment-related deaths. The toxicity that did occur was limited and low-grade, consisting mainly of mild xerostomia, or dry mouth, a well-known consequence of PSMA-targeted radioligand therapy caused by PSMA expression in the salivary glands. This favorable tolerability profile is significant because patients with recurrent glioma have often already endured intensive radiation and chemotherapy, leaving limited reserve for additional myelosuppressive treatment. The absence of hematologic toxicity in this small series suggests that the 100 kBq/kg dose level can be delivered safely, though the authors caution that larger cohorts are needed to characterize the full toxicity profile.

The theranostic framework underlying the trial deserves particular attention. Theranostics pairs a diagnostic imaging agent with a therapeutic compound sharing the same molecular target, allowing clinicians to confirm target expression before committing a patient to treatment. In this study, [⁶⁸Ga]-PSMA PET served as the companion diagnostic, identifying which lesions expressed PSMA on their vasculature and would therefore be expected to accumulate the alpha-emitting therapeutic. This personalized selection process, now standard in prostate cancer radioligand therapy following the success of lutetium-177 PSMA-617, could in principle spare glioma patients from ineffective treatment while concentrating clinical trials on the subset of tumors most likely to respond.

Significant hurdles remain before this approach can move toward routine clinical use. Alpha-emitting radiopharmaceuticals pose unique challenges, including the global scarcity of actinium-225, which is produced in limited quantities at only a handful of accelerator facilities worldwide, a constraint documented in recent mapping studies of global alpha-emitter production. The decay daughters of actinium-225 can also break free from their chelator and redistribute to normal organs, particularly the kidneys and salivary glands, a phenomenon that preclinical dosimetry studies are actively working to quantify and mitigate. Delivery to brain tumors is further complicated by the blood-brain barrier, although the vascular targeting strategy may partially circumvent this obstacle because the tumor neovasculature lies on the accessible side of the barrier. Optimal dose, cycle number, and combination with other therapies all remain to be defined.

Earlier targeted alpha therapy studies in glioma, including trials of actinium-225 and bismuth-213 labeled substance P analogues delivered directly into resection cavities, have demonstrated that alpha radiation can achieve long-term tumor control in selected patients, and reports of durable responses in low-grade gliomas have fueled interest in expanding these approaches. The present study extends the concept to systemic administration, which is far simpler logistically and could theoretically address both the primary lesion and distant tumor satellites. The Istanbul team, which received no external funding for the work and declared no competing interests, conducted the study with institutional ethics approval and informed consent from all participants, in accordance with the Declaration of Helsinki.

For now, the message from this pilot experience is one of measured hope. Systemic [²²⁵Ac]-PSMA therapy appeared feasible and well tolerated in patients who had exhausted conventional options, and it produced preliminary evidence of disease control in PSMA-expressing recurrent high-grade glioma. The authors and observers of the field alike stress that these findings must be validated in larger, controlled studies with longer follow-up before any claims of clinical benefit can be made. Yet the convergence of several trends, including expanding global production of actinium-225, improving PSMA PET imaging of brain tumors, and growing clinical experience with alpha radioligand therapy, suggests that targeted alpha therapy may be poised to become a genuine new frontier in the treatment of one of medicine’s most lethal cancers. If subsequent trials confirm and extend these early signals, the theranostic pairing of PSMA imaging with alpha-emitting therapy could offer patients with recurrent glioma something they have rarely had: a precisely targeted, systemically deliverable option with real potential to alter the course of their disease.

Subject of Research: Systemic targeted alpha therapy using actinium-225 labeled PSMA radioligand for recurrent high-grade glioma

Article Title: Targeted alpha therapy for recurrent high-grade glioma with [²²⁵Ac]-PSMA: a new theranostic approach

Article References: Sayman, H. B., Aras, O., Hekim, M. V., Sağlam, K., Akgün, E., & Dinçbaş, F. Ö. (2026). Targeted alpha therapy for recurrent high-grade glioma with [²²⁵Ac]-PSMA: a new theranostic approach. European Journal of Nuclear Medicine and Molecular Imaging. https://doi.org/10.1007/s00259-026-08194-6

Image Credits: AI Generated

DOI: 10.1007/s00259-026-08194-6

Keywords: glioblastoma, high-grade glioma, targeted alpha therapy, actinium-225, PSMA, theranostics, radioligand therapy, PET imaging, recurrent brain tumor, nuclear medicine, alpha emitters, PSMA-targeted therapy