Neurooncol Rev. 2026 Oct 31;28(26).



	Neuro-Oncology Reviews

	Volume 28 Number 26 - Special issue* 31 October 2026

	Home > Publications > Neuro-Oncology Reviews > Volume 28, Year 2026 > Number 26, 31 October


	The effects of radiotherapy on postoperative glioblastoma progression and recurrence. Educational annotated bibliography
	Radiotherapy has two simultaneous biological consequences: it reduces tumour burden, while creating selective and environmental pressures that influence the residual disease.


	Introduction

	A. Clinical foundations: efficacy and treatment resistance. Evidence for surgery plus radiotherapy versus surgery alone.

	Frankel SA, German WJ. Glioblastoma multiforme; review of 219 cases with regard to natural history, pathology, diagnostic methods, and treatment. J Neurosurg. 1958 Sep;15(5):489-503. doi: 10.3171/jns.1958.15.5.0489. PMID: 13576192. ˍ
	Annotation: A major historical retrospective series examining 219 patients with glioblastoma treated between 1924 and 1952. The study is particularly relevant to the early clinical evaluation of surgical treatment, including the relationship between extensive resection, partial resection and external decompression and subsequent survival. Its historical importance lies in the early recognition of the prognostic relevance of the extent of surgical intervention. However, retrospective design, selection bias, differences in tumour operability and the absence of modern diagnostic and molecular classification prevent a causal interpretation of the survival differences. Early use of radiotherapy on 47 patients.

	Edland RW, Javid M, Ansfield FJ. Glioblastoma multiforme. An analysis of the results of postoperative radiotherapy alone versus radiotherapy and concomitant 5-fluorouracil. (A prospective randomized study of 32 cases). Am J Roentgenol Radium Ther Nucl Med. 1971 Feb;111(2):337-42. doi: 10.2214/ajr.111.2.337. PMID: 5100220. Randomized Clinical Trial. ˍ
	Annotation: Design: Prospective randomized study, 32 patients. Comparison: Postoperative radiotherapy alone versus radiotherapy combined with 5- fluorouracil (5-FU). Contribution: One of the early attempts to improve the efficacy of radiation through pharmacological radiosensitization. Critical assessment: Very small sample; the study cannot establish a reliable survival advantage from adding 5-FU. Its importance is primarily historical.

	Andersen AP. Postoperative irradiation of glioblastomas. Results in a randomized series. Acta Radiol Oncol Radiat Phys Biol. 1978 Jan;17(6):475-84. doi: 10.3109/02841867809128178. PMID: 216238. Randomized Clinical Trial. ˍ
	Annotation: Design: Randomized study of 108 patients with glioblastoma, comparing surgery alone with surgery followed by postoperative radiotherapy. This is the closest match to the question because the comparison was specifically between the two treatment strategies. Finding: The study reported a survival advantage for postoperative irradiation. It is a particularly important historical reference because it directly addresses whether surgery alone is sufficient. Critical limitation: The trial is old, predates modern magnetic resonance imaging (MRI), molecular classification and contemporary radiotherapy, and is small by current standards. Its results should be interpreted in their historical context.

	Walker MD, Alexander E Jr, Hunt WE, MacCarty CS, Mahaley MS Jr, Mealey J Jr, Norrell HA, Owens G, Ransohoff J, Wilson CB, Gehan EA, Strike TA. Evaluation of BCNU and/or radiotherapy in the treatment of anaplastic gliomas. A cooperative clinical trial. J Neurosurg. 1978 Sep;49(3):333-43. doi: 10.3171/jns.1978.49.3.0333. PMID: 355604. Randomized Clinical Trial. ˍ
	Annotation: Design: Prospective randomized study of 303 patients with anaplastic gliomas, approximately 90% of whom had glioblastoma in the historical classification. Results: In the evaluable population, median survival was reported as approximately 35– 37.5 weeks with radiotherapy-containing treatment, compared with 14 weeks with conventional supportive care. Radiotherapy alone also outperformed chemotherapy alone. Critical limitation: The control group received supportive care rather than a uniformly defined modern surgery-alone protocol. The study nevertheless provides important randomized evidence that postoperative radiotherapy materially improves survival.

	Walker MD, Green SB, Byar DP, Alexander E Jr, Batzdorf U, Brooks WH, Hunt WE, MacCarty CS, Mahaley MS Jr, Mealey J Jr, Owens G, Ransohoff J 2nd, Robertson JT, Shapiro WR, Smith KR Jr, Wilson CB, Strike TA. Randomized comparisons of radiotherapy and nitrosoureas for the treatment of malignant glioma after surgery. N Engl J Med. 1980 Dec 4;303(23):1323-9. doi: 10.1056/NEJM198012043032303. PMID: 7001230. Randomized Clinical Trial. ˍ
	Annotation: Design: Randomized trial of 467 patients with histologically confirmed malignant glioma after surgery. Results: Radiotherapy-containing treatment arms demonstrated a survival advantage over semustine alone. The study helped establish radiotherapy as a central component of postoperative treatment. Critical limitation: This was not a pure surgery-alone comparison, and the histological categories do not map perfectly onto today's molecular definition of glioblastoma.

	Kristiansen K, Hagen S, Kollevold T, Torvik A, Holme I, Nesbakken R, Hatlevoll R, Lindgren M, Brun A, Lindgren S, Notter G, Andersen AP, Elgen K. Combined modality therapy of operated astrocytomas grade III and IV. Confirmation of the value of postoperative irradiation and lack of potentiation of bleomycin on survival time: a prospective multicenter trial of the Scandinavian Glioblastoma Study Group. Cancer. 1981 Feb 15;47(4):649-52. doi: 10.1002/1097-0142(19810215)47:4<649::aid-cncr2820470405>3.0.co;2-w. PMID: 6164465. Randomized Clinical Trial. ˍ
	Annotation: Design: Prospective multicentre randomized study of 118 patients with grade III or IV astrocytomas. Results: Median survival with radiotherapy was approximately 10.2 months, compared with 5.2 months with supportive care. Adding bleomycin did not significantly improve survival over radiotherapy alone. Critical limitation: The population included different tumour grades, and the control was supportive care rather than surgery alone. It reinforces the radiotherapy effect but is not an exact two-arm comparison of the question posed.

	Stupp R, Mason WP, van den Bent MJ, Weller M, Fisher B, Taphoorn MJ, Belanger K, Brandes AA, Marosi C, Bogdahn U, Curschmann J, Janzer RC, Ludwin SK, Gorlia T, Allgeier A, Lacombe D, Cairncross JG, Eisenhauer E, Mirimanoff RO; European Organisation for Research and Treatment of Cancer Brain Tumor and Radiotherapy Groups; National Cancer Institute of Canada Clinical Trials Group. Radiotherapy plus concomitant and adjuvant temozolomide for glioblastoma. N Engl J Med. 2005 Mar 10;352(10):987-96. doi: 10.1056/NEJMoa043330. PMID: 15758009. EORTC trial 22981/26981 / NCIC trial CE.3. ˍ
	Annotation: The landmark EORTC-NCIC trial established the survival benefit of adding concomitant and adjuvant TMZ to radiotherapy. It provides the essential clinical baseline for any discussion of the adverse biological effects of radiation: possible treatment associated resistance must be evaluated against the demonstrated net benefit of the treatment regimen. Because radiation and TMZ were combined, the trial does not isolate radiation-specific molecular effects.

	Keime-Guibert F, Chinot O, Taillandier L, Cartalat-Carel S, Frenay M, Kantor G, Guillamo JS, Jadaud E, Colin P, Bondiau PY, Meneï P, Loiseau H, Bernier V, Honnorat J, Barrié M, Mokhtari K, Mazeron JJ, Bissery A, Delattre JY; Association of French-Speaking Neuro-Oncologists. Radiotherapy for glioblastoma in the elderly. N Engl J Med. 2007 Apr 12;356(15):1527-35. doi: 10.1056/NEJMoa065901. PMID: 17429084. Trial Registration ID: NCT00430911. ˍ
	Annotation: Design: Randomized trial comparing radiotherapy plus supportive care with supportive care alone in patients aged 70 years or older. The final glioblastoma analysis included 81 patients. Results: Median survival was 29.1 weeks with radiotherapy versus 16.9 weeks with supportive care. The hazard ratio (HR) for death was 0.47 (95% confidence interval [CI], 0.29–0.76; 𝑃 = 0.002P=0.002). Critical limitation: The comparator was supportive care, not surgery alone. Nevertheless, the trial demonstrated that radiotherapy can provide a survival benefit even in older patients.

	Stupp R, Hegi ME, Mason WP, van den Bent MJ, Taphoorn MJ, Janzer RC, Ludwin SK, Allgeier A, Fisher B, Belanger K, Hau P, Brandes AA, Gijtenbeek J, Marosi C, Vecht CJ, Mokhtari K, Wesseling P, Villa S, Eisenhauer E, Gorlia T, Weller M, Lacombe D, Cairncross JG, Mirimanoff RO; European Organisation for Research and Treatment of Cancer Brain Tumour and Radiation Oncology Groups; National Cancer Institute of Canada Clinical Trials Group. Effects of radiotherapy with concomitant and adjuvant temozolomide versus radiotherapy alone on survival in glioblastoma in a randomised phase III study: 5-year analysis of the EORTC-NCIC trial. Lancet Oncol. 2009 Mar 9. 2009;10(5):459-66. doi: 10.1016/S1470-2045(09)70025-7. PMID: 19269895. Trial Registration ID: NCT00006353. ˍ
	Annotation: The five-year analysis confirmed the durable survival benefit of combined treatment, although long-term survivors remained a minority. The retrospective analysis of MGMT promoter methylation also established its importance as a predictor of benefit from alkylating chemotherapy. The paper is relevant when interpreting recurrence after standard treatment, but it does not establish whether radiation itself induces an aggressive recurrent phenotype.


	B. Experimental evidence: stem-like cells and radioresistance.

	Bao S, Wu Q, McLendon RE, Hao Y, Shi Q, Hjelmeland AB, Dewhirst MW, Bigner DD, Rich JN. Glioma stem cells promote radioresistance by preferential activation of the DNA damage response. Nature. 2006 Oct 18. 2006;444(7120):756-60. doi: 10.1038/nature05236. PMID: 17051156. ˍ
	Annotation: A foundational study demonstrating preferential activation of DNA-damage checkpoints and more effective repair of radiation-induced damage in CD133-positive glioma cells. The authors also reported enrichment of these cells after irradiation and showed that checkpoint inhibition could reverse aspects of their radioresistance. The findings support a mechanism by which treatment selects or preserves tumour-propagating cells. Limitations include reliance on particular stem-cell markers and experimental models; CD133 expression alone does not define all tumour-propagating cells.

	Kaur B, Khwaja FW, Severson EA, Matheny SL, Brat DJ, Van Meir EG. Hypoxia and the hypoxia-inducible-factor pathway in glioma growth and angiogenesis. Neuro Oncol. 2005 Apr 1;7(2):134-53. doi: 10.1215/S1152851704001115. PMID: 15831232. ˍ
	Annotation: A useful background reference for understanding how hypoxia, vascular abnormalities and hypoxia-inducible signalling contribute to glioma biology. Hypoxia is particularly relevant because it can reduce radiation effectiveness while activating adaptive survival pathways. This paper is not a direct demonstration that radiotherapy-induced hypoxia causes recurrence; it provides biological context for that hypothesis.


	C. Radiation-associated changes in the tumour microenvironment

	Barker HE, Paget JT, Khan AA, Harrington KJ. The tumour microenvironment after radiotherapy: mechanisms of resistance and recurrence. Nat Rev Cancer. 2015 Jun 2415(7):409-25. doi: 10.1038/nrc3958. PMID: 26105538. ˍ
	Annotation: An important conceptual framework for understanding radiation as both a cytotoxic intervention and a modifier of the tumour microenvironment. It examines hypoxia, vascular changes, inflammatory signalling and other mechanisms that may influence posttreatment tumour behaviour. Its breadth makes it useful for identifying hypotheses, but not every mechanism discussed is directly established in glioblastoma.

	Gupta K, Burns TC. Radiation-Induced Alterations in the Recurrent Glioblastoma Microenvironment: Therapeutic Implications. Front Oncol. 2018 Nov 8;8:503. doi: 10.3389/fonc.2018.00503. PMID: 30467536. ˍ
	Annotation: Particularly relevant to the present topic. It discusses how prior irradiation may produce persistent changes in extracellular matrix composition, vascular function, hypoxia, innate immune responses and cellular senescence. It proposes that some injury associated responses could provide a permissive environment for recurrent tumour growth. The authors appropriately frame many of these effects as mechanisms requiring further investigation, rather than established causes of clinical recurrence.


	D. Contemporary spatial and translational evidence

	Watson SS, Duc B, Kang Z, de Tonnac A, Eling N, Font L, Whitmarsh T, Massara M; iMAXT Consortium; Bodenmiller B, Hausser J, Joyce JA. Microenvironmental reorganization in brain tumors following radiotherapy and recurrence revealed by hyperplexed immunofluorescence imaging. Nat Commun. 2024 Apr 15;15(1):3226. doi: 10.1038/s41467-024-47185-9. PMID: 38622132. ˍ
	Annotation: This study uses high-dimensional spatial imaging to investigate radiation associated changes in immune-cell populations and tissue architecture in a preclinical glioblastoma model, including changes observed after treatment and during tumour regrowth. It is particularly valuable because it examines cellular organisation and interactions rather than relying exclusively on bulk gene-expression measurements. The observed treatment-associated changes provide a basis for mechanistic investigation, but a mouse model cannot establish the magnitude or causal importance of these processes in human recurrent glioblastoma.

	Rahman R, Shi DD, Reitman ZJ, Hamerlik P, de Groot JF, Haas-Kogan DA, D'Andrea AD, Sulman EP, Tanner K, Agar NYR, Sarkaria JN, Tinkle CL, Bindra RS, Mehta MP, Wen PY. DNA damage response in brain tumors: A Society for Neuro-Oncology consensus review on mechanisms and translational efforts in neuro-oncology. Neuro Oncol. 2024 Mar 22;26(8):1367-1387. doi: 10.1093/neuonc/noae072. PMID: 38770568. ˍ
	Annotation: A useful synthesis of DNA-damage response pathways and their therapeutic implications in brain tumours, including glioblastoma. It places radiation resistance in the wider context of DNA repair, treatment combinations, biomarker development and translational drug development. It is especially helpful for identifying candidate pathways for radiosensitisation, while highlighting the gap between promising laboratory findings and successful clinical translation.

	Debbi K, Loganadane G, To N, Cherif MA, Boukhobza C, Rida H, Grellier N, Mammar H, Belkacemi Y. New approaches to overcome radioresistance in glioblastoma: mechanisms, targets and role of innovative therapies, new particles and non-photon radiotherapy in 2024. A systematic review. Rep Pract Oncol Radiother. 2025 Apr 18;30(2):269-281. doi: 10.5603/rpor.105654. PMID: 40635989. ˍ
	Annotation: A broad review of approaches intended to overcome glioblastoma radioresistance, including DNA-damage response targets, hypoxia-related mechanisms and alternative radiation modalities. It is useful for extending the bibliography towards translational interventions. The existence of a plausible radiosensitising mechanism, however, should not be equated with clinical efficacy; results from different models, radiation schedules and combination regimens must be assessed separately.

	Sarrazin E, Valable S, Pérès EA, Colloc'h N, Emery E, Lesueur P, Leclerc A, Bernaudin M, Aury-Landas J. Glioblastoma and resistance to radiotherapy: role of cancer stem cells subpopulations, hypoxia and therapeutic strategies. Cancer Treat Rev. 2026 Aug 1;149:103198. doi: 10.1016/j.ctrv.2026.103198. PMID: 42659714. ˍ
	Annotation: A recent synthesis focused on the interactions between glioma stem-like cell states, hypoxia and radiation resistance. Its emphasis on cellular-state transitions is relevant to the distinction between selection of pre-existing resistant cells and treatmentassociated adaptation. As a review, it should be used to identify and trace primary studies rather than as a substitute for evaluating the underlying experiments individually.


	1. Selection versus induction in recurrent glioblastoma: pre-existing resistant clones or radiation-induced cellular states?

	A. Experimental foundations: radioresistance and cellular-state transitions

	Bao S, Wu Q, McLendon RE, Hao Y, Shi Q, Hjelmeland AB, Dewhirst MW, Bigner DD, Rich JN. Glioma stem cells promote radioresistance by preferential activation of the DNA damage response. Nature. 2006 Oct 18. 2006;444(7120):756-60. doi: 10.1038/nature05236. PMID: 17051156. ˍ
	Annotation: A foundational investigation demonstrating preferential activation of DNAdamage checkpoint responses in glioma stem-like cells following irradiation. The study provides evidence for differential survival of pre-existing cell populations and supports the hypothesis that cells with stem-like properties contribute to radioresistance. It is primarily evidence for selection and intrinsic resistance, rather than definitive proof that radiation induces a new resistant lineage. Its reliance on particular markers and experimental models limits direct extrapolation to the diversity of human glioblastoma.

	Bhat KPL, Balasubramaniyan V, Vaillant B, Ezhilarasan R, Hummelink K, Hollingsworth F, Wani K, Heathcock L, James JD, Goodman LD, Conroy S, Long L, Lelic N, Wang S, Gumin J, Raj D, Kodama Y, Raghunathan A, Olar A, Joshi K, Pelloski CE, Heimberger A, Kim SH, Cahill DP, Rao G, Den Dunnen WFA, Boddeke HWGM, Phillips HS, Nakano I, Lang FF, Colman H, Sulman EP, Aldape K. Mesenchymal differentiation mediated by NF-κB promotes radiation resistance in glioblastoma. Cancer Cell. 2013 Aug 29;24(3):331-46. doi: 10.1016/j.ccr.2013.08.001. PMID: 23993863. ˍ
	Annotation: One of the most relevant primary studies for the induction hypothesis. The authors demonstrated that a subset of proneural glioma stem-like cultures could acquire mesenchymal characteristics through TNF-α/NF-κB-dependent signalling, accompanied by a more radioresistant phenotype. The work also connected macrophage/microglial signals with mesenchymal differentiation. Its principal strength is the functional investigation of a candidate transition mechanism. However, the findings do not establish that radiation alone induces this transition in human tumours or that the mechanism dominates recurrence clinically.

	Neftel C, Laffy J, Filbin MG, Hara T, Shore ME, Rahme GJ, Richman AR, Silverbush D, Shaw ML, Hebert CM, Dewitt J, Gritsch S, Perez EM, Gonzalez Castro LN, Lan X, Druck N, Rodman C, Dionne D, Kaplan A, Bertalan MS, Small J, Pelton K, Becker S, Bonal D, Nguyen QD, Servis RL, Fung JM, Mylvaganam R, Mayr L, Gojo J, Haberler C, Geyeregger R, Czech T, Slavc I, Nahed BV, Curry WT, Carter BS, Wakimoto H, Brastianos PK, Batchelor TT, Stemmer-Rachamimov A, Martinez-Lage M, Frosch MP, Stamenkovic I, Riggi N, Rheinbay E, Monje M, Rozenblatt-Rosen O, Cahill DP, Patel AP, Hunter T, Verma IM, Ligon KL, Louis DN, Regev A, Bernstein BE, Tirosh I, Suvà ML. An Integrative Model of Cellular States, Plasticity, and Genetics for Glioblastoma. Cell. 2019 Jul 18;178(4):835-849.e21. doi: 10.1016/j.cell.2019.06.024. PMID: 31327527. ˍ
	Annotation: A major framework for understanding glioblastoma as a heterogeneous population of malignant cells occupying different, partially plastic transcriptional states. The study shows how genetic alterations and environmental influences shape the distribution of these states. It is essential for interpreting recurrence because it demonstrates why a change in phenotype need not imply a new genetic clone. It is not, however, a direct demonstration of radiation-induced state conversion in patients.

	Dirkse A, Golebiewska A, Buder T, Nazarov PV, Muller A, Poovathingal S, Brons NHC, Leite S, Sauvageot N, Sarkisjan D, Seyfrid M, Fritah S, Stieber D, Michelucci A, Hertel F, Herold-Mende C, Azuaje F, Skupin A, Bjerkvig R, Deutsch A, Voss-Böhme A, Niclou SP. Stem cell-associated heterogeneity in Glioblastoma results from intrinsic tumor plasticity shaped by the microenvironment. Nat Commun. 2019 Apr 16;10(1):1787. doi: 10.1038/s41467-019-09853-z. PMID: 30992437. ˍ
	Annotation: Particularly important for distinguishing a stable, intrinsically resistant subpopulation from a reversible phenotype. The study found that cells expressing stemcell-associated markers could alter their phenotype in response to environmental conditions, with multiple populations capable of contributing to tumour growth. This challenges a rigid hierarchical model in which only a permanently defined stem-cell compartment can regenerate the tumour. The experiments do not establish that radiation is the principal driver of the observed plasticity.


	B. Genetic selection and clonal evolution

	Johnson BE, Mazor T, Hong C, Barnes M, Aihara K, McLean CY, Fouse SD, Yamamoto S, Ueda H, Tatsuno K, Asthana S, Jalbert LE, Nelson SJ, Bollen AW, Gustafson WC, Charron E, Weiss WA, Smirnov IV, Song JS, Olshen AB, Cha S, Zhao Y, Moore RA, Mungall AJ, Jones SJM, Hirst M, Marra MA, Saito N, Aburatani H, Mukasa A, Berger MS, Chang SM, Taylor BS, Costello JF. Mutational analysis reveals the origin and therapy-driven evolution of recurrent glioma. Science. 2013 Dec 12;343(6167):189-193. doi: 10.1126/science.1239947. PMID: 24336570. ˍ
	Annotation: An important study of evolutionary relationships between initial and recurrent gliomas. It demonstrated that recurrent tumours may emerge from early-diverging populations and that TMZ exposure can be associated with hypermutation and therapy related mutational signatures. The cohort included lower-grade gliomas that progressed, rather than exclusively adult-type glioblastomas; it is therefore best used as a conceptual and comparative reference for clonal evolution. Its findings support the need to distinguish pre-existing clones from treatment-associated mutagenesis, but they do not establish radiation-specific causality.

	Al-Holou WN, Wang H, Ravikumar V, Shankar S, Oneka M, Fehmi Z, Verhaak RG, Kim H, Pratt D, Camelo-Piragua S, Speers C, Wahl DR, Hollon T, Sagher O, Heth JA, Muraszko KM, Lawrence TS, de Carvalho AC, Mikkelsen T, Rao A, Rehemtulla A. Subclonal evolution and expansion of spatially distinct THY1-positive cells is associated with recurrence in glioblastoma. Neoplasia. 2023 Jan 6;36:100872. doi: 10.1016/j.neo.2022.100872. PMID: 36621024. ˍ
	Annotation: Particularly strong evidence for a selection-based mechanism. The authors identified THY1-positive mesenchymal/stem-like cells in untreated glioblastoma, demonstrated relative resistance to chemoradiotherapy in experimental models, and observed marked enrichment of this population at recurrence. Their experiments also implicated transforming growth factor-β (TGF-β) signalling in maintaining the associated phenotype and resistance. The findings support the expansion of pre-existing resistant cells, potentially from spatially restricted niches. Nevertheless, the combined use of radiation and TMZ prevents clean attribution to either treatment, and enrichment does not exclude additional state transitions during recurrence.


	C. Human longitudinal single-cell evidence

	Wang L, Jung J, Babikir H, Shamardani K, Jain S, Feng X, Gupta N, Rosi S, Chang S, Raleigh D, Solomon D, Phillips JJ, Diaz AA. A single-cell atlas of glioblastoma evolution under therapy reveals cell-intrinsic and cell-extrinsic therapeutic targets. Nat Cancer. 2022 Dec 20;3(12):1534-1552. doi: 10.1038/s43018-022-00475-x. PMID: 36539501. ˍ
	Annotation: A key study of matched primary and recurrent glioblastomas, combining single nucleus RNA sequencing, chromatin analysis, DNA sequencing and spatial approaches. The investigators reported a shift towards mesenchymal-like states at recurrence and identified signalling relationships between malignant cells and their microenvironment. Crucially, the observed shift could reflect selection of pre-existing mesenchymal cells, induction of a mesenchymal programme in other cells, or differential proliferation. This makes the study central to the question, but its observational human component cannot independently determine the relative contribution of selection and induction.

	Spitzer A, Johnson KC, Nomura M, Garofano L, Nehar-Belaid D, Darnell NG, Greenwald AC, Bussema L, Oh YT, Varn FS, D'Angelo F, Gritsch S, Anderson KJ, Migliozzi S, Gonzalez Castro LN, Chowdhury T, Robine N, Reeves C, Park JB, Lipsa A, Hertel F, Golebiewska A, Niclou SP, Nusrat L, Kellet S, Das S, Moon HE, Paek SH, Bielle F, Laurenge A, Di Stefano AL, Mathon B, Picca A, Sanson M, Tanaka S, Saito N, Ashley DM, Keir ST, Ligon KL, Huse JT, Yung WKA, Lasorella A, Iavarone A, Verhaak RGW, Tirosh I, Suvà ML. Deciphering the longitudinal trajectories of glioblastoma ecosystems by integrative single-cell genomics. Nat Genet. 2025 May 9;57(5):1168-1178. doi: 10.1038/s41588-025-02168-4. PMID: 40346362. ˍ
	Annotation: This investigation examined matched primary and recurrent IDH-wildtype glioblastomas from 59 patients. Unlike a model predicting a uniform mesenchymal shift, the study found substantial heterogeneity in the trajectories of malignant-cell states, with no single state consistently enriched across the entire cohort. It provides important counterbalancing evidence to studies suggesting a common recurrence-associated phenotype. Differences between primary and recurrent samples can reflect treatment effects, baseline tumour biology, spatial sampling and changes in the surrounding brain tumour ecosystem. The study strengthens the case for patient-specific evolutionary trajectories but cannot alone distinguish radiation-induced transitions from selection.


	2. Microenvironmental causality: which radiation-associated changes in microglia, macrophages, astrocytes, vasculature and extracellular matrix actually increase tumour growth when functionally perturbed?

	A. Microglia and macrophages: radiation-induced signals that support regrowth

	Kioi M, Vogel H, Schultz G, Hoffman RM, Harsh GR, Brown JM. Inhibition of vasculogenesis, but not angiogenesis, prevents the recurrence of glioblastoma after irradiation in mice. J Clin Invest. 2010 Feb 22;120(3):694-705. doi: 10.1172/JCI40283. PMID: 20179352. ˍ
	Annotation: A landmark study linking post-irradiation hypoxia to the recruitment of bone marrow-derived cells, particularly CD11b-positive myelomonocytic cells, and subsequent restoration of functional tumour vasculature. The investigators inhibited hypoxia-inducible factor 1 (HIF-1), the stromal cell-derived factor 1 (SDF-1)/C-X-C chemokine receptor 4 (CXCR4) axis, or myeloid-cell recruitment and observed reduced or delayed tumour regrowth. The study provides strong preclinical evidence that a radiation-associated tissue response can causally support recurrence. Its main limitation is that the xenograft models and the definition of recruited cells do not fully capture the complexity of human microglia and macrophage populations. It also investigates a coupled myeloid–vascular mechanism rather than isolating a single macrophage phenotype.

	Alberghina C, Torrisi F, D'Aprile S, Longhitano L, Giallongo S, Scandura G, Mannino G, Mele S, Sabini MG, Cammarata FP, Russo G, Abdelhameed AS, Zappalà A, Lo Furno D, Giuffrida R, Li Volti G, Tibullo D, Vicario N, Parenti R. Microglia and glioblastoma heterocellular interplay sustains tumour growth and proliferation as an off-target effect of radiotherapy. Cell Prolif. 2024 Mar 7;57(6):e13606. doi: 10.1111/cpr.13606. PMID: 38454614. ˍ
	Annotation: Directly addresses the possibility that radiation affects non-malignant microglia in ways that support surviving tumour cells. The authors found that conditioned media from irradiated human microglia increased proliferation of radiation-naïve glioblastoma cell lines and altered tumour-cell metabolic behaviour. In contrast, conditioned media from irradiated glioblastoma cells produced different, in some conditions cytotoxic, effects. This distinction is important: the response of the microenvironment cannot be inferred from the response of the malignant cells themselves. The work demonstrates paracrine sufficiency in vitro, but it does not establish which secreted factor is necessary for the effect or whether the same mechanism drives recurrence in vivo.

	Barker HE, Paget JT, Khan AA, Harrington KJ. The tumour microenvironment after radiotherapy: mechanisms of resistance and recurrence. Nat Rev Cancer. 2015 Jun 24;15(7):409-25. doi: 10.1038/nrc3958. PMID: 26105538. ˍ
	Annotation: A foundational framework for interpreting radiation-induced changes in immune cells, vasculature, extracellular matrix and inflammatory signalling. It is valuable for generating hypotheses about microenvironmental causality, but evidence from other tumour types should not automatically be extrapolated to glioblastoma.


	B. Astrocytes and senescence: the irradiated brain as a permissive niche

	Fletcher-Sananikone E, Kanji S, Tomimatsu N, Di Cristofaro LFM, Kollipara RK, Saha D, Floyd JR, Sung P, Hromas R, Burns TC, Kittler R, Habib AA, Mukherjee B, Burma S. Elimination of Radiation-Induced Senescence in the Brain Tumor Microenvironment Attenuates Glioblastoma Recurrence. Cancer Res. 2021 Sep 27;81(23):5935-5947. doi: 10.1158/0008-5472.CAN-21-0752. PMID: 34580063. ˍ
	Annotation: Particularly relevant to astrocyte-mediated effects. The investigators found that cranial irradiation induced widespread cellular senescence, with astrocytes particularly susceptible. Irradiated brain tissue showed increased expression of the cell-cycle regulator CDKN1A (p21) and senescence-associated secretory phenotype (SASP) factors, including hepatocyte growth factor (HGF). Pre-irradiation of the brain enhanced growth and invasiveness of subsequently implanted glioma cells in a MET-dependent setting. The work moves beyond correlation by linking an irradiated tissue environment to tumour behaviour and investigating the relevant signalling pathway. Important limitations include the use of preclinical models and the difficulty of determining how much of the effect is attributable to astrocytes versus other senescent brain cells.

	Gupta K, Burns TC. Radiation-Induced Alterations in the Recurrent Glioblastoma Microenvironment: Therapeutic Implications. Front Oncol. 2018 Nov 8;8:503. doi: 10.3389/fonc.2018.00503. PMID: 30467536. ˍ
	Annotation: This review integrates radiation-associated neuroinflammation, astrocyte reactivity, microglial responses, extracellular-matrix remodelling, vascular abnormalities and senescence. It is useful for tracing primary references and identifying interactions between injury responses and tumour progression. Its proposed integrated model is biologically plausible, but several pathways are supported by different experimental systems rather than by one experiment establishing the entire causal chain. It should therefore be used as a map of hypotheses, not as proof that every radiation-associated change promotes recurrence.


	C. Vasculature and vascular-like tumour cells

	Kioi M, Vogel H, Schultz G, Hoffman RM, Harsh GR, Brown JM. Inhibition of vasculogenesis, but not angiogenesis, prevents the recurrence of glioblastoma after irradiation in mice. J Clin Invest. 2010 Feb 22;120(3):694-705. doi: 10.1172/JCI40283. PMID: 20179352. ˍ
	Annotation: This is the key primary reference for the hypothesis that radiation-induced vascular damage creates a hypoxic environment that recruits circulating myeloid and other bone-marrow-derived cells, enabling vascular restoration and tumour regrowth. The study's importance lies in its functional interventions: interfering with recruitment or signalling substantially delayed recurrence. However, the finding should not be simplified into the claim that all post-radiation angiogenesis is tumour-promoting. The authors specifically distinguished vasculogenesis from angiogenesis, and the relevance of these mechanisms depends on model, timing and cellular definitions.

	Muthukrishnan SD, Kawaguchi R, Nair P, Prasad R, Qin Y, Johnson M, Wang Q, VanderVeer-Harris N, Pham A, Alvarado AG, Condro MC, Gao F, Gau R, Castro MG, Lowenstein PR, Deb A, Hinman JD, Pajonk F, Burns TC, Goldman SA, Geschwind DH, Kornblum HI. P300 promotes tumor recurrence by regulating radiation-induced conversion of glioma stem cells to vascular-like cells. Nat Commun. 2022 Oct 19;13(1):6202. doi: 10.1038/s41467-022-33943-0. PMID: 36261421. ˍ
	Annotation: An important extension of the vascular hypothesis. The authors reported that radiation can induce glioma stem-like cells to acquire endothelial-like and pericyte-like characteristics. These vascular-like cells provided trophic support for tumour-cell proliferation, and their selective depletion reduced post-treatment tumour growth in vivo. The study implicated the histone acetyltransferase p300 in radiation-associated chromatin remodelling and the acquisition of vascular-associated programmes. This is stronger than a simple observation of increased vascular markers because it includes functional depletion and pathway inhibition. Nevertheless, the extent to which this phenomenon contributes to human recurrence, compared with recruitment of non-malignant vascular and myeloid cells, remains unresolved.


	D. Extracellular matrix and coagulation-associated remodelling

	Jeon HM, Kim JY, Cho HJ, Lee WJ, Nguyen D, Kim SS, Oh YT, Kim HJ, Jung CW, Pinero G, Joshi T, Hambardzumyan D, Sakaguchi T, Hubert CG, McIntyre TM, Fine HA, Gladson CL, Wang B, Purow BW, Park JB, Park MJ, Nam DH, Lee J. Tissue factor is a critical regulator of radiation therapy-induced glioblastoma remodeling. Cancer Cell. 2023 Jul 13 14;41(8):1480-1497.e9. doi: 10.1016/j.ccell.2023.06.007. PMID: 37451272. ˍ
	Annotation: This study identified CD142/tissue factor (F3) as a radiation-induced feature of senescence-associated β-galactosidase-positive glioblastoma cells. Tissue factor promoted clonal expansion of irradiated cells and was linked to both tumour-cell autonomous signalling and extrinsic coagulation pathways. The authors reported mesenchymal-like state changes, chemokine secretion, tumour-associated macrophage activation and extracellular-matrix remodelling. Its strength is the proposed connection between an irradiated tumour-cell state and several microenvironmental consequences. The study does not mean that every observed downstream change is independently necessary for recurrence; the contribution of coagulation, macrophages and matrix remodelling needs to be evaluated pathway by pathway.

	Gupta K, Burns TC. Radiation-Induced Alterations in the Recurrent Glioblastoma Microenvironment: Therapeutic Implications. Front Oncol. 2018 Nov 8;8:503. doi: 10.3389/fonc.2018.00503. PMID: 30467536. ˍ
	Annotation: This review discusses changes in matrix composition and turnover, including matrix metalloproteinases, basement-membrane components, adhesion molecules and integrin-associated signalling. It proposes that these changes can alter invasion, tissue architecture and the interaction between glioma cells and their surrounding brain. It is a useful source for identifying matrix-related targets, but it does not provide a single definitive demonstration that radiation-induced extracellular-matrix remodelling is necessary for human recurrence. Direct evidence requires selective inhibition or restoration of a defined matrix component in an irradiated glioma model.


	E. Spatial and cellular mapping after radiotherapy

	Watson SS, Duc B, Kang Z, de Tonnac A, Eling N, Font L, Whitmarsh T, Massara M; iMAXT Consortium; Bodenmiller B, Hausser J, Joyce JA. Microenvironmental reorganization in brain tumors following radiotherapy and recurrence revealed by hyperplexed immunofluorescence imaging. Nat Commun. 2024 Apr 15;15(1):3226. doi: 10.1038/s41467-024-47185-9. PMID: 38622132. ˍ
	Annotation: This study examines changes in cellular composition and tissue organisation after irradiation and during tumour regrowth. In one glioma model, the authors observed increased tumour-associated myeloid cells, T cells and fibroblast-like populations after radiation, together with a temporary increase in extracellular-matrix-rich regions. The regrowing tumours partially recapitulated the cellular landscape of untreated tumours, demonstrating that the post-treatment microenvironment is dynamic rather than a fixed radiation-induced state. This is valuable descriptive and spatial evidence, but it does not establish that each enriched cell population or matrix-rich region promotes growth. Functional perturbation is needed to identify the causal components.

	Berg TJ, Pietras A. Radiotherapy-induced remodeling of the tumor microenvironment by stromal cells. Semin Cancer Biol. 2022 Feb 8;86(Pt 3):846-856. doi: 10.1016/j.semcancer.2022.02.011. PMID: 35143991. ˍ
	Annotation: A useful synthesis of radiation effects on endothelial cells, vasculature, macrophages, microglia, astrocytes and the extracellular matrix, with particular attention to glioblastoma. It explains why non-malignant stromal cells exposed during treatment can activate repair responses that may inadvertently support tumour progression. As a review, it is best used to trace and compare the underlying primary studies rather than as direct evidence of causality.


	3. Longitudinal human evidence: can paired primary and recurrent tumour samples, spatial profiling and single-cell analyses distinguish radiation effects from temozolomide, surgery and natural tumour evolution?

	A. Genomic evolution of primary and recurrent glioma

	Johnson BE, Mazor T, Hong C, Barnes M, Aihara K, McLean CY, Fouse SD, Yamamoto S, Ueda H, Tatsuno K, Asthana S, Jalbert LE, Nelson SJ, Bollen AW, Gustafson WC, Charron E, Weiss WA, Smirnov IV, Song JS, Olshen AB, Cha S, Zhao Y, Moore RA, Mungall AJ, Jones SJM, Hirst M, Marra MA, Saito N, Aburatani H, Mukasa A, Berger MS, Chang SM, Taylor BS, Costello JF. Mutational analysis reveals the origin and therapy-driven evolution of recurrent glioma. Science. 2013 Dec 12;343(6167):189-193. doi: 10.1126/science.1239947. PMID: 24336570. ˍ
	Annotation: A foundational study demonstrating that recurrent gliomas can arise from early diverging populations and that the recurrent tumour's mutation profile may differ substantially from that of the original specimen. It established the importance of reconstructing evolutionary relationships rather than interpreting every recurrence associated mutation as newly acquired. The major limitation for the present question is that the study focused on lower-grade gliomas and their progression, rather than exclusively on adult-type glioblastoma after standard chemoradiotherapy. It is best regarded as an evolutionary framework, not direct evidence of radiation-specific effects.

	Kim H, Zheng S, Amini SS, Virk SM, Mikkelsen T, Brat DJ, Grimsby J, Sougnez C, Muller F, Hu J, Sloan AE, Cohen ML, Van Meir EG, Scarpace L, Laird PW, Weinstein JN, Lander ES, Gabriel S, Getz G, Meyerson M, Chin L, Barnholtz-Sloan JS, Verhaak RG. Whole-genome and multisector exome sequencing of primary and post-treatment glioblastoma reveals patterns of tumor evolution. Genome Res. 2015 Feb 3;25(3):316-27. doi: 10.1101/gr.180612.114. PMID: 25650244. ˍ
	Annotation: Particularly useful for understanding the effects of spatial heterogeneity on evolutionary inference. By examining multiple regions and comparing pretreatment with post-treatment disease, the study showed that the clonal structure of glioblastoma can be more complex than a simple linear progression from one dominant clone. The inclusion of multisector sampling helps reveal alterations that might be missed in a single biopsy. However, treatment histories were not uniform across all cases, and post-treatment genomic changes cannot be assigned uniquely to radiation, TMZ or natural evolution.

	Touat M, Li YY, Boynton AN, Spurr LF, Iorgulescu JB, Bohrson CL, Cortes-Ciriano I, Birzu C, Geduldig JE, Pelton K, Lim-Fat MJ, Pal S, Ferrer-Luna R, Ramkissoon SH, Dubois F, Bellamy C, Currimjee N, Bonardi J, Qian K, Ho P, Malinowski S, Taquet L, Jones RE, Shetty A, Chow KH, Sharaf R, Pavlick D, Albacker LA, Younan N, Baldini C, Verreault M, Giry M, Guillerm E, Ammari S, Beuvon F, Mokhtari K, Alentorn A, Dehais C, Houillier C, Laigle-Donadey F, Psimaras D, Lee EQ, Nayak L, McFaline-Figueroa JR, Carpentier A, Cornu P, Capelle L, Mathon B, Barnholtz-Sloan JS, Chakravarti A, Bi WL, Chiocca EA, Fehnel KP, Alexandrescu S, Chi SN, Haas-Kogan D, Batchelor TT, Frampton GM, Alexander BM, Huang RY, Ligon AH, Coulet F, Delattre JY, Hoang-Xuan K, Meredith DM, Santagata S, Duval A, Sanson M, Cherniack AD, Wen PY, Reardon DA, Marabelle A, Park PJ, Idbaih A, Beroukhim R, Bandopadhayay P, Bielle F, Ligon KL. Mechanisms and therapeutic implications of hypermutation in gliomas. Nature. 2020 Apr 15;580(7804):517-523. doi: 10.1038/s41586-020-2209-9. PMID: 32322066. ˍ
	Annotation: An essential reference for separating TMZ-associated evolution from radiation associated changes. The authors characterised hypermutation in gliomas, including recurrent tumours with mismatch-repair abnormalities following alkylating-agent exposure. The work links treatment history, molecular evolution and resistance, and illustrates how a specific treatment can impose a recognisable selective and mutational pressure. It does not provide a universal molecular test that separates all radiation effects from TMZ effects, but it establishes an important framework for identifying the contribution of alkylating agent-associated evolution.


	B. Single-cell analysis of treatment-associated evolution

	Neftel C, Laffy J, Filbin MG, Hara T, Shore ME, Rahme GJ, Richman AR, Silverbush D, Shaw ML, Hebert CM, Dewitt J, Gritsch S, Perez EM, Gonzalez Castro LN, Lan X, Druck N, Rodman C, Dionne D, Kaplan A, Bertalan MS, Small J, Pelton K, Becker S, Bonal D, Nguyen QD, Servis RL, Fung JM, Mylvaganam R, Mayr L, Gojo J, Haberler C, Geyeregger R, Czech T, Slavc I, Nahed BV, Curry WT, Carter BS, Wakimoto H, Brastianos PK, Batchelor TT, Stemmer-Rachamimov A, Martinez-Lage M, Frosch MP, Stamenkovic I, Riggi N, Rheinbay E, Monje M, Rozenblatt-Rosen O, Cahill DP, Patel AP, Hunter T, Verma IM, Ligon KL, Louis DN, Regev A, Bernstein BE, Tirosh I, Suvà ML. An Integrative Model of Cellular States, Plasticity, and Genetics for Glioblastoma. Cell. 2019 Jul 18;178(4):835-849.e21. doi: 10.1016/j.cell.2019.06.024. PMID: 31327527. ˍ
	Annotation: Although not primarily a longitudinal treatment study, this paper is essential for interpreting changes between primary and recurrent tumours. It demonstrates that malignant cells can occupy several transcriptional states, influenced by both genetic alterations and environmental signals. Consequently, a recurrent tumour may exhibit a different cellular-state composition without requiring the emergence of a new genetic clone. The work provides a conceptual basis for distinguishing clonal evolution from phenotypic adaptation, but it cannot independently determine whether radiotherapy, TMZ or surgery caused a specific transition.

	Wang L, Jung J, Babikir H, Shamardani K, Jain S, Feng X, Gupta N, Rosi S, Chang S, Raleigh D, Solomon D, Phillips JJ, Diaz AA. A single-cell atlas of glioblastoma evolution under therapy reveals cell-intrinsic and cell-extrinsic therapeutic targets. Nat Cancer. 2022 Dec 20;3(12):1534-1552. doi: 10.1038/s43018-022-00475-x. PMID: 36539501. ˍ
	Annotation: One of the most important studies for this research question. The investigators profiled primary and recurrent glioblastoma specimens using single-nucleus RNA sequencing, chromatin accessibility analysis, DNA sequencing and spatial transcriptomic/proteomic methods. They identified a shift towards a mesenchymal-like phenotype in recurrent disease, associated with activator protein 1 (AP-1) signalling, and described interactions between malignant cells, neuroglia and immune populations. The study provides compelling evidence that the cellular ecosystem changes during treatment and recurrence. However, the authors recognised several possible explanations for the mesenchymal shift: preferential survival of cells already in that state, transition of other cells into it, or differential proliferation. Because recurrent samples had been exposed to standard treatment, the study cannot attribute all observed changes to radiotherapy alone.

	Spitzer A, Johnson KC, Nomura M, Garofano L, Nehar-Belaid D, Darnell NG, Greenwald AC, Bussema L, Oh YT, Varn FS, D'Angelo F, Gritsch S, Anderson KJ, Migliozzi S, Gonzalez Castro LN, Chowdhury T, Robine N, Reeves C, Park JB, Lipsa A, Hertel F, Golebiewska A, Niclou SP, Nusrat L, Kellet S, Das S, Moon HE, Paek SH, Bielle F, Laurenge A, Di Stefano AL, Mathon B, Picca A, Sanson M, Tanaka S, Saito N, Ashley DM, Keir ST, Ligon KL, Huse JT, Yung WKA, Lasorella A, Iavarone A, Verhaak RGW, Tirosh I, Suvà ML. Deciphering the longitudinal trajectories of glioblastoma ecosystems by integrative single-cell genomics. Nat Genet. 2025 May 9;57(5):1168-1178. doi: 10.1038/s41588-025-02168-4. PMID: 40346362. ˍ
	Annotation: This study is particularly important because it qualifies the idea of a universal recurrence-associated mesenchymal shift. Using matched primary and recurrent IDHwildtype glioblastomas, the investigators found considerable variation in malignant-cell- state trajectories. No single state was consistently enriched across the cohort, although specific trajectories were evident in subsets of patients. The most consistent change was a reduced malignant-cell fraction accompanied by an increased relative abundance of glial and neuronal cells in the sampled tumour ecosystem. These findings suggest that cellular-state changes at recurrence are patient-specific and closely linked to baseline tumour properties and the surrounding microenvironment. They also demonstrate why smaller cohorts can yield apparently different conclusions. As with other paired human studies, the analysis cannot independently separate radiation effects from TMZ, surgery and natural evolution.


	C. Multimodal profiling and spatial organisation

	Lucas CG, Al-Adli NN, Young JS, Gupta R, Morshed RA, Wu J, Ravindranathan A, Shai A, Oberheim Bush NA, Taylor JW, de Groot J, Villanueva-Meyer JE, Pekmezci M, Perry A, Bollen AW, Theodosopoulos PV, Aghi MK, Chang EF, Hervey-Jumper SL, Raleigh DR, Molinaro AM, Costello JF, Diaz AA, Clarke JL, Butowski NA, Phillips JJ, Chang SM, Berger MS, Solomon DA. Longitudinal multimodal profiling of IDH-wildtype glioblastoma reveals the molecular evolution and cellular phenotypes underlying prognostically different treatment responses. Neuro Oncol. 2024 Nov 19;27(1):89-105. doi: 10.1093/neuonc/noae214. PMID: 39560080. ˍ
	Annotation: This investigation evaluated paired initial and recurrent glioblastomas from 106 patients. It found that some early genomic alterations were retained between initial and recurrent tumours, whereas many other alterations were present at only one time point. The study also demonstrated heterogeneous epigenomic evolution, with tumours showing increased methylation, decreased methylation or relative stability. Sarcomatous transformation and TMZ-associated hypermutation were associated with distinct molecular and clinical patterns. Its strength is the size of the paired cohort and integration of several molecular layers. It provides a more comprehensive view of tumour evolution than a single-assay study. Nevertheless, because the samples were obtained following standard treatment, the findings do not independently establish which changes were induced by radiotherapy, TMZ, surgery or spontaneous progression.

	Ajaib S, Winter-Luke J, Digby RJ, Pollock S, Hemmings G, Gusnanto A, Chakrabarty A, Ismail A, Wilson E, Hunter B, Filby A, McDonald D, Brockman AA, Ihrie RA, Stead LF. Spatial profiling of longitudinal glioblastoma reveals consistent changes in cellular architecture, post-treatment. Neuro Oncol. 2025 Sep 1;27(12):3145-3160. doi: 10.1093/neuonc/noaf190. PMID: 40898767. ˍ
	Annotation: This study used imaging mass cytometry to examine cellular composition and spatial interactions in paired primary and recurrent specimens from five patients, with validation using a separate spatial transcriptomic platform. It reported changes in cellular prevalence and architecture after treatment, including a reduction in vascular-cell prevalence and an increased proportion of normal brain cells in the sampled recurrent tissue. The principal contribution is spatial: the study investigates where cells are located and how their relationships change, rather than relying exclusively on bulk tumour averages. Its very small cohort, however, limits generalisability. Moreover, spatial changes between diagnosis and recurrence remain associations with the entire treatment and evolutionary interval; they do not establish the independent causal contribution of radiotherapy.


	4. Therapeutic translation: can specific resistance mechanisms be targeted without compromising the established benefits of radiotherapy or causing unacceptable injury to normal brain tissue?

	A. Established treatment and the biological basis of radioresistance

	Stupp R, Mason WP, van den Bent MJ, Weller M, Fisher B, Taphoorn MJ, Belanger K, Brandes AA, Marosi C, Bogdahn U, Curschmann J, Janzer RC, Ludwin SK, Gorlia T, Allgeier A, Lacombe D, Cairncross JG, Eisenhauer E, Mirimanoff RO; European Organisation for Research and Treatment of Cancer Brain Tumor and Radiotherapy Groups; National Cancer Institute of Canada Clinical Trials Group. Radiotherapy plus concomitant and adjuvant temozolomide for glioblastoma. N Engl J Med. 2005 Mar 10;352(10):987-96. doi: 10.1056/NEJMoa043330. PMID: 15758009. EORTC trial 22981/26981 / NCIC trial CE.3. ˍ
	Annotation: The landmark trial establishing concomitant and adjuvant temozolomide with radiotherapy as a standard regimen for newly diagnosed glioblastoma. Median overall survival was 14.6 months with combined treatment versus 12.1 months with radiotherapy alone. This is the essential clinical benchmark for radiosensitization research: an experimental intervention should preserve the established benefits of the standard regimen.

	Bao S, Wu Q, McLendon RE, Hao Y, Shi Q, Hjelmeland AB, Dewhirst MW, Bigner DD, Rich JN. Glioma stem cells promote radioresistance by preferential activation of the DNA damage response. Nature. 2006 Oct 18. 2006;444(7120):756-60. doi: 10.1038/nature05236. PMID: 17051156. ˍ
	Annotation: A seminal study showing that glioma stem-like cells can preferentially activate DNA-damage checkpoints and repair radiation-induced damage. Inhibiting checkpoint kinases Chk1 and Chk2 reversed radioresistance in experimental systems. The work provides a mechanistic rationale for targeting DNA-damage responses, but it does not establish that this approach improves survival in patients or that it is safe for normal neural stem-cell populations.

	Bhat KPL, Balasubramaniyan V, Vaillant B, Ezhilarasan R, Hummelink K, Hollingsworth F, Wani K, Heathcock L, James JD, Goodman LD, Conroy S, Long L, Lelic N, Wang S, Gumin J, Raj D, Kodama Y, Raghunathan A, Olar A, Joshi K, Pelloski CE, Heimberger A, Kim SH, Cahill DP, Rao G, Den Dunnen WFA, Boddeke HWGM, Phillips HS, Nakano I, Lang FF, Colman H, Sulman EP, Aldape K. Mesenchymal differentiation mediated by NF-κB promotes radiation resistance in glioblastoma. Cancer Cell. 2013 Aug 29;24(3):331-46. doi: 10.1016/j.ccr.2013.08.001. PMID: 23993863. ˍ
	Annotation: This study linked NF-κB-associated mesenchymal differentiation with radiation resistance. It supports investigation of state-associated transcriptional programmes rather than assuming resistance is exclusively genetic. However, mesenchymal-like states are heterogeneous and plastic, and blocking a single transcriptional programme may not prevent alternative resistant states from emerging.


	B. DNA-damage-response inhibitors: translational promise and limitations

	Rahman R, Shi DD, Reitman ZJ, Hamerlik P, de Groot JF, Haas-Kogan DA, D'Andrea AD, Sulman EP, Tanner K, Agar NYR, Sarkaria JN, Tinkle CL, Bindra RS, Mehta MP, Wen PY. DNA damage response in brain tumors: A Society for Neuro-Oncology consensus review on mechanisms and translational efforts in neuro-oncology. Neuro Oncol. 2024 Mar 22;26(8):1367-1387. doi: 10.1093/neuonc/noae072. PMID: 38770568. ˍ
	Annotation: A particularly useful starting point for evaluating inhibitors of DNA-dependent protein kinase (DNA-PK), PARP, checkpoint kinases and other DNA-damage-response pathways. It discusses target biology, preclinical models, biomarkers, combination strategies and clinical-trial design. The review also illustrates why mechanistic rationale does not reliably predict clinical benefit: drug exposure, combination toxicity and tumourspecific vulnerabilities must be considered together.

	Sim HW, McDonald KL, Lwin Z, Barnes EH, Rosenthal M, Foote MC, Koh ES, Back M, Wheeler H, Sulman EP, Buckland ME, Fisher L, Leonard R, Hall M, Ashley DM, Yip S, Simes J, Khasraw M. A randomized phase II trial of veliparib, radiotherapy, and temozolomide in patients with unmethylated MGMT glioblastoma: the VERTU study. Neuro Oncol. 2021 May 13;23(10):1736-1749. doi: 10.1093/neuonc/noab111. PMID: 33984151. Trial registration ID: ACTRN12615000407594. ˍ
	Annotation: One of the most instructive clinical tests of a radiosensitizing strategy. The trial randomized 125 patients with newly diagnosed, MGMT-unmethylated glioblastoma to a veliparib-containing regimen or standard radiotherapy plus temozolomide. Six-month progression-free survival was 46% versus 31%, respectively, but median overall survival was 12.7 versus 12.8 months. The investigators concluded that there was insufficient evidence of clinical benefit. The important lesson is not that PARP inhibition can never work in GBM. Rather, a favourable preclinical interaction and acceptable feasibility do not establish a meaningful survival benefit. Biomarker selection, the specific drug schedule and the contribution of each treatment component remain important questions.

	Aiyappa-Maudsley R, Chalmers AJ, Parsons JL. Factors affecting the radiation response in glioblastoma. Neurooncol Adv. 2022 Sep 25;4(1):vdac156. doi: 10.1093/noajnl/vdac156. PMID: 36325371. ˍ
	Annotation: Reviews DNA repair, hypoxia, tumour heterogeneity, metabolism and other determinants of radiation response, including the rationale for inhibiting DNA-PK. Its discussion of normal-brain toxicity is particularly relevant: DNA repair is not a tumourexclusive process, and increasing the radiation sensitivity of normal tissues could narrow the therapeutic window. This reference is useful when assessing whether an inhibitor should advance from cell-based experiments to in vivo testing.


	C. Targeting the tumour microenvironment and radiation-associated recovery

	Barker HE, Paget JT, Khan AA, Harrington KJ. The tumour microenvironment after radiotherapy: mechanisms of resistance and recurrence. Nat Rev Cancer. 2015 Jun 2415(7):409-25. doi: 10.1038/nrc3958. PMID: 26105538. ˍ
	Annotation: A broad framework for understanding how radiotherapy affects not only tumour cells but also vasculature, stromal cells, immune populations and tissue signalling. It is not a GBM-only review, so individual mechanisms must be validated specifically in glioblastoma. Its central contribution is conceptual: radiation can simultaneously damage tumour cells and remodel the environment in which surviving cells persist.

	Kioi M, Vogel H, Schultz G, Hoffman RM, Harsh GR, Brown JM. Inhibition of vasculogenesis, but not angiogenesis, prevents the recurrence of glioblastoma after irradiation in mice. J Clin Invest. 2010 Feb 22;120(3):694-705. doi: 10.1172/JCI40283. PMID: 20179352. ˍ
	Annotation: In mouse glioblastoma models, the authors investigated hypoxia-associated recruitment of myelomonocytic cells and vascular restoration after irradiation. Interfering with this process delayed or prevented recurrence in the experimental systems. The study provides a mechanistic rationale for targeting specific post-radiation recovery pathways rather than simply intensifying radiation. The limitations are important: a causal effect in a mouse model does not prove that the same mechanism dominates human recurrence. Moreover, blocking vascular or myeloid-cell responses could compromise normal tissue recovery, depending on the pathway, timing and degree of inhibition.

	Fletcher-Sananikone E, Kanji S, Tomimatsu N, Di Cristofaro LFM, Kollipara RK, Saha D, Floyd JR, Sung P, Hromas R, Burns TC, Kittler R, Habib AA, Mukherjee B, Burma S. Elimination of Radiation-Induced Senescence in the Brain Tumor Microenvironment Attenuates Glioblastoma Recurrence. Cancer Res. 2021 Sep 27;81(23):5935-5947. doi: 10.1158/0008-5472.CAN-21-0752. PMID: 34580063. ˍ
	Annotation: Investigates radiation-associated cellular senescence in the brain tumour microenvironment and the potential contribution of senescence-associated secretory signalling to recurrence. The reported experimental findings support investigating senescent stromal cells and their secreted factors as potential therapeutic targets. The translation problem is selectivity: senescence can be harmful in some contexts but also contributes to tumour suppression, wound healing and tissue repair. A clinically useful intervention would need to eliminate or inhibit the relevant tumour-promoting signals without indiscriminately disrupting beneficial senescence responses in normal tissue.


	D. Wider therapeutic landscape

	Ali MY, Oliva CR, Noman ASM, Allen BG, Goswami PC, Zakharia Y, Monga V, Spitz DR, Buatti JM, Griguer CE. Radioresistance in Glioblastoma and the Development of Radiosensitizers. Cancers (Basel). 2020 Sep 3;12(9):2511. doi: 10.3390/cancers12092511. PMID: 32899427. ˍ
	Annotation: A useful overview of proposed radiosensitization approaches, covering DNA repair, glioma stem-like cells, hypoxia, metabolic adaptation and the tumour microenvironment. It helps organize the field into candidate mechanisms, but the strength of evidence differs substantially among targets. The proposed interventions should not be interpreted as equally mature or clinically validated.

	Van Eupen L, Waked A, Primac I, Vermeulen K, De Bie I, Benotmane MA, Quintens R. Innovative radiotherapies for the treatment of glioblastoma. Neurooncol Adv. 2025 Dec 8;8(1):vdaf255. doi: 10.1093/noajnl/vdaf255. PMID: 41684714. ˍ
	Annotation: Discusses approaches to improving radiotherapy in GBM, including strategies informed by tumour heterogeneity and plasticity. It is relevant to the broader question of whether the therapeutic ratio can be improved through changes in radiation delivery or by combining radiotherapy with biologically targeted approaches. It should be read alongside, rather than as a substitute for, clinical trial data demonstrating safety and survival benefit.






	*AI assistance: This issue was prepared with the assistance of ChatGPT (OpenAI). The editor is solely responsible for the final content.