State of the neoadjuvant therapy for glioblastoma multiforme—Where do we stand?

Abstract Glioblastoma multiforme (GBM) is the most common malignant primary brain tumor in adults. Despite several investigations in this field, maximal safe resection followed by chemoradiotherapy and adjuvant temozolomide with or without tumor-treating fields remains the standard of care with poor survival outcomes. Many endeavors have failed to make a dramatic change in the outcomes of GBM patients. This study aimed to review the available strategies for newly diagnosed GBM in the neoadjuvant setting, which have been mainly neglected in contrast to other solid tumors.

nant primary tumor of the central nervous system in adults. 1,2ts annual age-adjusted incidence ranges between 0.59 and 5 per 100,000 population worldwide. 3GBM is considered one of the most aggressive, invasive, and undifferentiated types of brain cancer.The 5-year survival rate is only 5.6% which represents the aggressive manner of this pathology. 1aximal safe resection followed by concurrent chemoradiotherapy and adjuvant temozolomide (TMZ) for 6 cycles form the current standard of care for GBM.This combination of postoperative therapies is collectively known as the "Stupp protocol." 4 Surgery, preferably gross total resection (GTR) or even a supratotal resection due to its positive impact on the outcomes, is the gold standard surgical procedure for GBM. 5,6It confirms the diagnosis, provides tissue for molecular analysis, and improving the symptoms by quickly reducing the mass effect.Unfortunately, GTR might not be feasible depending on the location or the technical limitations, and partial resection or even biopsy may be offered to some patients. 7Even if the GTR is possible, the infiltrative nature of GBM makes the surgery per se insufficient for achieving a definitive cure. 8In fact, without multimodality adjuvant treatment, the overall survival (OS) is very low. 9adiation therapy (RT) eliminates microscopic residual disease at the primary site in the vicinity of the grossly resected lesion or the unresected macroscopic residual tumor so that it can maximize the chances of local control. 10However, RT is limited by the surrounding anatomical structures with a known dose tolerance. 11RT is delivered using one of the 3D conformal or intensity-modulated radiotherapy (IMRT) or volumetric modulated arc therapy techniques to a standard dose of 60Gy in 30 fractions, with hypofractionated regimens reserved for elderly or fragile patients (40Gy/15 or 20Gy/5). 12,13he standard chemotherapy includes oral TMZ, given concurrently with RT at a daily dose of 75 mg/m 2 from the first to the last day of RT, followed by an adjuvant dose of 150-200 mg/ m 2 for 5 days up to 6 cycles which are repeated every 4 weeks.The prospective studies following Stupp failed to show added benefit from extension of TMZ cycles to one year or 12 cycles. 14n addition, drug development studies have been largely unsuccessful after TMZ due to the presence of the blood-brain barrier (BBB), which prevents most cytotoxic agents from accumulating in the brain. 15fter the landmark EF-14 trial, tumor treating field (TTF) has also been approved by the United States Food and Drug Association (US FDA) for the postoperative setting after CRT and concomitant by the maintenance TMZ. 16By delivering alternating low-intensity electric fields, TTF interferes with the mitotic activity of GBM cells and confers progression-free survival (PFS) and overall survival (OS) benefits.However, its use has remained very low even in academic referral sites for neuro-oncology practice. 17ollowing the establishment of the standard of care in GBM, there have been some investigational modifications to improve the outcomes in patients.For example, the addition of lomustine to the RT plus TMZ in methylated MGMT patients was a successful maneuver in the phase III CeTeG/NOA-09 trial. 18However, due to the small sample size and other limitations, this trial was not been able to change the standard of care so far.
Other than RT, TMZ, and TTF, adjunctive treatments suggested for GBM have been tested or proposed that include targeted therapies and immunotherapy (IO), Boron neutron capture therapy (BNCT) and epigenetic therapy, oncolytic virus therapy (OV), and gene therapy.None of these treatments has become the standard of care for the primary GBM treatment as yet.Many of these adjunctive therapies are still in the preclinical state, some were tested in the clinical settings and were ineffective or needed more evidence to integrate with the standard of care.
BNCT is a modality for biochemical adjunctive therapies in which boron is delivered using a selective vector to the neoplastic tissue.Because of the damaged BBB or augmented expression of the amino acid transporters on the tumor cell surface, boron only concentrates in the tumor.Then, neutron particles are irradiated from an external device, and then boron and neutron react in the tumor cell.This process theoretically provides normal tissue-sparing and high-dose radiation delivery.Efforts in BNCT of brain tumors started in 2002, and available results demonstrate the beneficial effect of such therapy on the survival of patients with both recurrent and newly diagnosed glioblastomas. 19ncolytic virotherapy (OV), a subgroup of immunotherapy (IO), is another landscape studied in clinical trials with overall safety but variable efficacy.OV is based on converting the immunogenically "cold" brain tumors to "hot" ones that stimulate the immune system.There are two types of oncolytic viruses.The first type, called replication-competent, includes the viruses that invade the tumor cell and start replication until cell death.Then, the replicated viruses can invade other tumor cells and evoke an immune response due to the release of massive tumor cell antigens.The second type, selectively replication-competent, includes viruses used as vectors to apply gene therapy. 20So far, only Teserpaturev/G47 Delta, a replication-competent recombinant herpes simplex virus, has received conditional and time-limited approval from the Japanese authorities for use in gliomas based on the GD-01 phase II trial. 21nother investigational treatment for GBM is gene therapy, defined as inserting a mutated gene or transcript in the tumor cells by way of mRNAs or in combination with nanoparticles. 22Gene therapies that impact GBM cells with specific mutations seem more popular in ongoing trials.
One treatment approach that is so attractive in other solid tumors is targeted therapies using monoclonal antibodies or small molecule tyrosine kinase inhibitors (TKI).Numerous medications have been tested in this regard, and all have been unsuccessful except bevacizumab and BRAF inhibitors, which showed some activity in phase II but unfortunately not in phase III trials. 23,24he latest trendy approach for the treatment of GBM has been the use of an immune checkpoint inhibitor (ICI).ICIs upregulate immune response and reveal the concealed tumor cell to the immune system.So, the body itself can eliminate it.In practice, however, despite the positive results of phase I Checkmate-143, which showed safety and some promising findings, 25 the phase III Checkmate-498 and Checkmate-548 trials disastrously failed.In Checkmate-498 in exclusively unmethylated MGMT patients, nivolumab plus RT was significantly inferior to TMZ and RT in terms of OS. 26 Seemingly, in Checkmate-548 in methylated MGMT patients, the addition of nivolumab to RT plus TMZ could not increase OS and PFS despite increased toxicity. 27The failure of ICIs, which is attributable to the immunologic coldness of brain tumors, have made investigators combine ICI with OV-based therapies, as described above, to see whether it can improve results.CAPTIVE phase I/II trial tested a single intratumoral injection of an oncovirus called DNX-2401 combined with intravenous multiple doses of pembrolizumab in recurrent GBM with a promising 1-year OS rate of about 52%. 28ngoing trials are in way testing if this approach has efficacy in the primary GBM as well.
Despite all the mentioned maneuvers, median overall survival is slightly more than one year from diagnosis, so that even in the most favorable situations, the majority of patients do not survive beyond 2 years. 4An area that has been less investigated and merits more attention is neoadjuvant therapy (NAT).NAT is defined as applying another effective treatment before the main local treatment, which is surgery or RT in most cancers.NAT has been shown to improve clinical outcomes in many solid malignancies. 29So, in the following sections, we review the current neoadjuvant treatment strategies for newly diagnosed and recurrent GBM.We have been focusing on their feasibility, safety, and efficacy and describing future directions in this field.

Methods
The characteristics and results of original retrospective and prospective studies investigating the efficacy of neoadjuvant therapies for patients with resectable or unresectable GBM (primary or recurrent) were reviewed.1][32] Also, studies conducted before the approval of chemoradiation as the standard of care for newly diagnosed GBM in 2005 were not included. 4oadjuvant Therapy for Newly Diagnosed GBM NAT has been established as a standard of care in many primary solid malignancies.For example, in rectal cancer where the bony pelvis limits surgical resection, it has been proved that pre-operative or NAT confers lower toxicity and better sphincter preservation than post-op or adjuvant therapy. 33The German Rectal Cancer Study group's trial was the most important study that made the pre-op CRT vs. post-op CRT the standard of care in rectal cancer. 34With preoperative CRT compared to the postoperative treatment, there was a statistically significant decrease in local failure and a significant decrease in acute toxicity and late complications.Nevertheless, even with an 11-year follow-up, there was still no effect on OS or distant Nabian et al.: State of the neoadjuvant therapy for GBM metastases. 35We brought the rectal cancer example to emphasize the possible role of NAT in the milieu of a limited surgical resection.This phenomenon is shared between rectal cancer and GBM.
There are theoretical benefits to NAT that are evident in other solid tumors such as soft tissue sarcoma, breast, esophagus, or rectal cancer, with implications in GBM.The use of neoadjuvant treatment has the following justifications: (a) in case of response to NAT, the resultant down-sizing of the tumor would make the surgery easier with less damage to normal surrounding tissues. 36In case of GBM, this can result in less extensive surgery with subsequent better outcomes; (b) in terms of neoadjuvant RT, we can see the gross target volume so the target delineation can be done more confidently, the target volume is smaller due to absence of a surgical bed, better oxygenation of the unmanipulated tissues requiring less dose to exert the same effects, and removal of much of irradiated tissue during surgery that would decrease the chance of radionecrosis and subsequently less toxicity of RT 37 ; (c) the sensitivity of the systemic agents would be tested in the final surgical specimen so that the adjuvant treatment can be tailored based on the response; (d) clinical trials could be designed on response to therapy as a surrogate of more long-term outcomes. 38All of these benefits have replaced the adjuvant with neoadjuvant treatment as the new standard of care in rectal, esophageal, and gastric cancer and the preferred treatment in high-risk breast cancer and soft-tissue sarcoma.In some instances, NAT is done using systemic therapy alone or in conjunction with RT.
The role of NAT for GBM has been explored in phase I/ II studies and has yet to be established as a standard of care.To commence a neoadjuvant treatment for GBM, we need a confirmed tissue diagnosis or highly suggestive imaging diagnosis with highly accurate thoughts on the tumor's molecular profile.These requirements are major challenges in opting for a de-facto NAT for GBM.
First, repeated craniotomy to primarily obtain the tissue samples for a definite diagnosis and identification of the molecular profile and subsequently to resect the residual tumor following NAT would be challenging.Neurosurgical interventions are sophisticated procedures that pose significant operative risks to the patient, namely hemorrhage and infection.To address this concern as an obstacle to NAT, one may propose a stereotactic biopsy to obtain the tissue before commencing treatment. 39However, its inherent complexity and need for high-tech devices and skilled neurosurgeons make stereotactic biopsy a nonreadily accessible modality.Thus, this modality should be considered before commencing preoperative therapy to collect samples.
Second, although imaging can accurately define a brain mass lesion as a high-grade glioma, it cannot distinguish GBM from other high-grade gliomas (HGG) or a solitary brain metastasis of an unknown origin. 40Considering the improvements in magnetic resonance imaging (MRI), including new sequences and techniques for image acquisition, it is easier to establish a diagnosis of HGG with high accuracy; this may obviate the urgent need to collect tissue for histological diagnosis.Based on its unique imaging characteristics, it is also possible to define the tumor's molecular profile using advanced MRI techniques, such as apparent diffusion coefficient and relative cerebral blood flow.In addition, major recent developments in the fields of radiomics and radiogenomics have made it possible to predict the response of GBM to specific therapies accurately. 41With continuous growth in this field, radiological imaging with new MRI sequences can provide additional tools for improving HGG diagnosis.In cases where biopsy/surgical resection is not feasible, or NAT is planned to be delivered, radiology can also aid in the tumoral profiling of tumors.However, its role is more pronounced in lower-grade gliomas, such as detecting isocitrate dehydrogenase (IDH)-1/2 mutation. 42Another useful imaging modality is the positron emission tomography-computed tomography (PET-CT) scan.PET-CT has shown more sensitivity but lower specificity than advanced brain MRI, although the difference was non-significant. 43PET-CT with 18F-fluciclovin tracer may find small satellite tumors with a diameter below the usual PET resolution, not noted on MRI. 44Although some studies found PET-CT helpful in distinguishing recurrent high-grade glioma from treatmentrelated changes (pseudoprogression and radionecrosis), further study is needed to address this topic.In general, the role of PET-CT in GBM is investigational.
An alternative for tissue sampling by surgery or biopsy is provided by obtaining a liquid biopsy from plasma or cerebrospinal fluid (CSF).This trending technique offers the advantage of being quicker and less invasive than the conventional brain biopsy while providing valuable diagnostic information.Both plasma-or CSF-based liquid biopsy procedures can identify circulating tumor cells, circulating tumor DNA, and circulating cell-free tumor RNA and discover disrupted signaling pathways to determine the molecular subtype of the tumor, and therefore, the prognosis and response to therapy.Since collecting plasma samples is straightforward for the clinicians and the patients, this method may also be used to monitor the treatment response and to follow-up the patient post-operatively. 45ereunder, we review the published literature on neoadjuvant therapies in 3 different newly diagnosed GBM scenarios: (i) preoperative therapy for GBM; (ii) postoperative neoadjuvant chemotherapy before standard chemoradiation for unresectable or inoperable GBM; and (iii) postoperative neoadjuvant systemic therapy before chemoradiation for resectable GBM; Preoperative Neoadjuvant Therapy for GBM Since the introduction of stereotactic techniques, there has been a renewed interest in studying preoperative RT for primary GBM. 46A phase I POBIG trial with awaited results tests the preoperative stereotactic radiosurgery followed by maximal safe resection and standard adjuvant CRT and TMZ. 47When it comes to preoperative systemic therapy, we only found 2 studies that looked into the impact of neoadjuvant chemotherapy on surgical results for those with GBM.This is shown in Table 1.The concerns raised and described in the section above might explain the scarcity of literature exploring NAT.
Razis et al. conducted a phase II clinical trial, exploring the efficacy of administration of oral imatinib before definitive surgery for newly diagnosed GBM.The endpoints included overall survival and comparison of the proliferation markers (Ki-67 and CD34) by immunohistochemistry in the pre and postsurgical samples, pharmacokinetics in liquid biopsies, and quantification of imatinib in surgical specimens.All patients underwent a CT-guided biopsy before the start of neoadjuvant imatinib.Median survival was 6.2 months.There was no indication of an impact on proliferation, as demonstrated by the absence of any change in Ki67 expression.The authors concluded that despite the presence of imatinib in the tumor samples and biochemical evidence of response to therapy by changes in activation of AKT and mitogen-activated protein kinase or p27 level in pre-and post-treatment specimens, there was no effect on the patients' survival nor proliferation of the tumor cells. 48n another study, Miyake et al. tested the efficacy of neoadjuvant bevacizumab (BEV) in a phase II randomized clinical trial among GBM patients with low Karnofsky performance status (KPS) or tumors located in eloquent areas. 49n this study, the investigators used neuronavigational techniques, including intra-operative MRI, MET-PET, FMISO-PET, FLT-PET, and 5-ALA together with preoperative BEV in 6 out of 12 patients.Using BEV made the resection time shorter, and the residual volume smaller in a way that more patients had >95% resection rate in the BEV group.The authors concluded that BEV improved patients' prognosis and outcomes in a preoperative setting.
Although no definite conclusions can be drawn based on these 2 trials, de-facto NAT may be a new promising approach for a subset of GBM patients with low KPS.At the same time, further research is needed to create more solid evidence.Actually, the study of preoperative therapies is strongly limited by the need for surgical diagnostic specimens.Thus, efforts should be focused on improving the radiological tools for non-surgical diagnoses in the future. 50evertheless, the expected benefit of BEV is not correlated with MGMT status. 51However, the usual benefit from IO or TKIs usually correlates with some molecular alterations in the tumoral tissue.

Postoperative Neoadjuvant Systemic Therapy Before Standard Chemoradiation for Unresectable or Inoperable GBM
As described earlier, surgical resection constitutes an integral part of GBM treatment together with RT and systemic therapy with or without TTF.However, surgery may be limited by the presence of various factors: (i) patientrelated such as low KPS score, advanced age, medical unfitness for surgery, or (ii) tumor-related such as multifocality, tumors localized in eloquent areas where resection is not feasible.In these cases, tumor diagnosis is based on stereotactic biopsy or neuroimaging.The overall prognosis in unresected tumors is dismal. 52The management includes RT, with or without concurrent and sequential chemotherapy or chemotherapy alone.In the case of bulky tumors, the target volume for RT due to its large size may cause increased side effects, in turn leading to decreased RT compliance.In addition, the necrotic inherence of extensive GBM tumors with severe hypo-oxygenation of tumor cells confers higher radioresistance, making the efficacy of irradiation more limited when compared to smallersize tumors. 53These limitations have led to the pursuit of neoadjuvant systemic therapy before the RT delivery.The rationale of this approach is that after the damage to the BBB, the anti-tumor agent can penetrate and concentrate more in the tumor and be more effective. 54Besides, delivering systemic agents with the ability to cross the BBB in a neoadjuvant setting offers the potential advantage of the tumor to shrink, thus decreasing the RT target volume with the benefit of less acute and late side effects.This reduction in volume may result in improved neurological symptoms after RT completion and, subsequently, patients' performance status.The latter is especially important for methylated MGMT cases with a better prognosis when treated with standard RT and concurrent TMZ.
On the contrary, initiating RT as soon as possible may be clinically beneficial to the patients by inducing tumor shrinkage in unresectable GBM and improving associated neurological symptoms.The true benefit of NAT has not been tested in a randomized setting and may prolong the median time from surgery to RT initiation.Nevertheless, Balaña et al. showed that prolongation caused by NAT was not an adverse prognostic factor for OS and that patients who started RT after the optimal cut-off duration of 6.43 weeks had a longer OS compared to those who began RT before this point (median 19.1 months vs. 6.6 months, P = .005) 55; therefore, the longer diagnosis-to-RT interval for delivering neoadjuvant chemotherapy might be not hazardous.
Studies investigating the benefits and toxicity of neoadjuvant postoperative systemic therapy before CRT as the primary adjuvant treatment using various regimens are represented in Table 2.  BEV: bevacizumab; IRI: irinotecan; TMZ: temozolomide; OS: overall survival; PFS: progression-free survival: RR: response rate; ORR: objective response rate; CON: concomitant; ADJ: adjuvant.
Barrie et al. evaluated the role of TMZ plus carmustine (BCNU) before and after RT in unresectable GBM patients.They showed that this regimen is safe and effective.The median OS was 12.7 months, and the median PFS was 7.4 months.Forty-two percent of patients had a partial or complete response, similar to the response rate of neoadjuvant TMZ only in sub-totally resected GBM patients. 56n the study by Chinot et al., biopsied-only patients with GBM received 4 cycles of TMZ alone (150 mg/m 2 /d on days 1-7 and on days 15-21 of every 28-day cycle (7 days on/7 days off)), before and after RT (60 Gy in 30 fractions).The objective response rate in patients with low MGMT methylation vs. high MGMT methylation was 55% vs. 7%, respectively (P = .004).High expression was defined as more than 35% of tumor cell nuclei expressing detectable MGMT protein; low expression was defined as less than 35%.PFS and OS were prolonged by 3.6 months (P = .009)and 11 months (P = .003),respectively, in patients with low vs. high MGMT expression.However, this result may be confounded by differences in the extent of RT in these subgroups.The authors concluded that neoadjuvant chemotherapy may be feasible for inoperable GBM patients with low MGMT methylation status. 57ihan et al. retrospectively evaluated the efficacy of BEV plus TMZ or fotemustine in poor-performance status patients with unresectable GBM as a bridge to standard chemoradiotherapy.Neoadjuvant treatment was delivered until maximal clinical and radiological response.The median OS was 12.5 months which was unusually high for these poor-performance patients.They concluded that rapid use of BEV plus TMZ helped improve the delivery of RT to a smaller area with a standard dose while sparing more unaffected brain tissue. 58n the study of Lou et al., patients received TMZ plus BEV before standard RT dose with concurrent TMZ + BEV.Median survival was 11.7 months.This combination was generally tolerable, though one potential study-related death was reported due to myocardial infarction (G5 toxicity).The authors concluded that TMZ and BEV in the neoadjuvant setting stabilized the gross disease in multifocal and unresectable GBM cases and merits further welldesigned phase III trials. 59hauffert et al. initiated a randomized phase II trial evaluating neoadjuvant BEV plus irinotecan (IRI) before CRT vs. adjuvant BEV and IRI.Despite higher 6-month PFS rates (50% vs. 30%), the OS was the same in both arms (median OS = 11.1 months).They concluded that the combination of neo-adjuvant and adjuvant BEV with IRI, TMZ, and RT is not recommended for further evaluation in the first-line treatment of unresectable GBM. 60apdevila et al. compared the results of 2 consecutive cohorts with unresectable GBM patients.The first cohort used 2 cycles of neoadjuvant chemotherapy (cisplatin plus TMZ) prior to local irradiation.In the second cohort, the established current standard CRT was done.Median PFS was not different between the 2 cohorts (3.3 vs. 5.1 months, P = NS).However, patients with methylated MGMT had a better outcome regarding PFS and OS with the neoadjuvant chemotherapy.Patients without MGMT methylation showed a better outcome regarding PFS and OS with upfront standard CRT.The authors concluded that neoadjuvant TMZ plus cisplatin has no positive or negative effect on the outcome of patients with unresectable GBM or anaplastic astrocytoma.Besides, adding cisplatin to the neoadjuvant regimen does not increase the benefit obtained from TMZ alone.They also highlighted the importance and possibility of integrating molecular testing into treatment planning. 30n the study by Peters et al., patients were treated with TMZ + BEV + IRI.Only 4.9% showed tumor progression.Median overall survival was 12 months, and median progression-free survival was 8.6 months (95% CI: 3.5-11.3months).They concluded that upfront treatment with BEV, TMZ, and IRI is tolerable and can lead to a radiographic response in unresectable or subtotally resected GBM. 61alana et al. compared neoadjuvant and concurrent TMZ with TMZ + BEV.Their primary endpoint was response assessment.The investigational treatment was more active than TMZ alone at the expense of greater toxicity.In the TMZ arm, the leading cause of NAT discontinuation was disease progression.In contrast, in the investigational arm, it was toxicity.Patients in the TMZ + BEV arm experienced more grade 1-2 stomatitis.Clinically significant intracranial hemorrhage occurred in 4 patients in the combination arm, including 2 deaths.A third patient in the TMZ + BEV arm died from intestinal perforation.There was no other significant difference in the frequency of toxicities between the two components.Although more patients suffered from toxicity in the combination arm, more patients completed the treatment, and neurological decline was more common in the TMZ arm.Eleven patients (24.5 %) in the TMZ arm and 29 (60.4 %) in the TMZ + BEV arm attained clinical benefit (partial response or stable disease).There was a trend toward better PFS (4.8 vs. 2.2 months) and OS (10.6 vs. 7.7 months) in the investigational arm.Although this study was not powered to detect differences in PFS or OS, it reached its primary endpoint of higher response.As in the TEMAVIR study, they found more intracranial hemorrhage in the BEV arm (4.2 % vs. none in the control arm). 62s described above, neoadjuvant chemotherapy in the biopsied-only GBM patients showed inconclusive results.This failure may be owed to administering different neoadjuvant regimens and variable control groups.A welldesigned randomized phase III trial is necessary to generate solid evidence with more robust conclusions-for instance, one comparing neoadjuvant TMZ ± BEV with the current standard of care.Integrating the MGMT status in the trial design is highly recommended to stratify the effect on treatment response and survival.

Postoperative Neoadjuvant Systemic Therapy Before Chemoradiation for Resectable GBM
It is well established that GBM represents an aggressive disease with a doubling time of 49.6 days. 63Therefore, given that time is essential, CRT after surgery as the standard of care has the disadvantage of allowing the tumor to develop and progress during the gap between surgery and RT start. 64This interval is influenced by several factors, including the availability of histopathological results, limited access to RT facilities, a waiting list for RT start, and post-op imaging uncertainties to define target volume for an accurate RT delivery.These factors all can Nabian et al.: State of the neoadjuvant therapy for GBM result in a negative impact on the patient's prognosis. 65his concern justifies the use of neoadjuvant systemic treatment for patients with newly diagnosed GBM.Using this treatment option, we can limit tumor progression, optimize the extent of tumor resection, and improve the patient's prognosis.
A summary of clinical trials investigating the efficacy of chemotherapy before CRT for patients with newly diagnosed resectable GBM is represented in Table 3.Other studies evaluating the effect of neoadjuvant chemotherapy on different types of glioma, such as low-grade glioma, 75,76 or studies that did not isolate GBM when evaluating HGG 77 were not included in this table, as we aimed only to review the treatment options for GBM.
First, Gruber et al. evaluated the efficacy and toxicity of postop neoadjuvant carboplatin in 25 patients.They demonstrated the feasibility and modest toxicity of the regimen. 78Gilbert et al. evaluated TMZ before RT alone.The objective response to TMZ treatment was 39%.In addition, 32% of patients had stable disease.They concluded that postop neoadjuvant TMZ is well tolerated and probably as effective as other more toxic chemotherapy agents like nitrosourea or cisplatin.They also proposed an evaluation of this regimen with CRT with TMZ in upcoming trials. 66hoi et al. evaluated ACNU and cisplatin and found that it is feasible to administer an intensive chemotherapy regimen to these patients.They saw that although the prognosis may be worse in patients with tumors growing during chemotherapy, some would stabilize after RT. 67 Kim et al. performed a prospective randomized controlled multicenter phase III trial to evaluate 2 cycles of neoadjuvant ACNU plus cisplatin (CDDP), followed by standard conventional radiotherapy followed by 6 cycles of adjuvant temozolomide as in the control group.The study was closed after an interim analysis of 82 patients due to a high frequency of toxic side effects despite promising actuarial survival outcomes.Although the median survival benefit in the treatment group over the control group was 9.5 months, this difference did not reach statistical significance (P = .2). Similarly, the progression-free survival was not different.Importantly, meta-analyses have confirmed the anti-cancer effects of nitrosourea compounds, including survival benefits.The authors concluded that neoadjuvant chemotherapy with ACNU-CDDP followed by radiotherapy and adjuvant temozolomide as primary treatment for GBM 68 So, the upcoming trials skipped using ACNU or CDDP.
Hodfland et al. randomized 65 patients to bevacizumabirinotecan (Bev-Iri) or bevacizumab-temozolomide (Bev-Tem) for 8 weeks, followed by concomitant CRT and adjuvant chemotherapy with Bev-Iri or Bev-Tem.They concluded that irinotecan has no benefit in first-line therapy compared to temozolomide.Moreover, only the Bev-Tem arm met the prespecified activity level of interest. 69ao et al. compared the standard TMZ regimen plus early post-surgery TMZ (early TMZ group) vs. the standard TMZ regimen (control group).Median OS time was 17.6 months in the early TMZ group and 13.2 months in the control group (P = .021).They mentioned that adding 2 weeks of TMZ starting the 14th day after surgery to the standard regimen can improve OS in GBM patients with similar AE and SAE occurrences. 70Shenouda et al. evaluated neo-adjuvant TMZ started 2-3 weeks following surgery at a daily dose of 75 mg/m 2 for 2 weeks before delivering HART (60 Gy in 20 daily fractions) with concurrent and adjuvant TMZ in 50 patients.Their study showed that this novel approach of neo-adjuvant TMZ is associated with encouraging favorable long-term survival with acceptable toxicity.A future comparative trial of the efficacy of this regimen is warranted. 71iang et al. retrospectively evaluated 375 patients with GBM.One hundred sixty-three patients received superearly TMZ within 7 days (SEG), while 212 received conventional protocol alone (CG).Due to the retrospective nature of the present study, they conducted propensity score matching to reduce the bias in patient selection and aimed to disclose the actual effect of the super-early initiation of TMZ.Final results showed that the median OS of patients in SEG was significantly prolonged without additional adverse effects compared with those in CG.This survival benefit was more prominent in patients with MGMT promoter methylation or non-GTR than vice versa.The adjusted hazard ratio for death in SEG was 0.60, indicating a 40% relative reduction in the risk of death for patients treated with super-early TMZ.Thus, they mentioned that perhaps 1 week after surgery is the ideal time window to initiate TMZ, especially for those with MGMT promoter methylation or non-GTR. 72s mentioned above, a few small sample-size studies have evaluated the efficacy and safety of neoadjuvant chemotherapy for patients with newly diagnosed GBM.The ORR varied between 12% and 42%; a stable disease was reported in 14-28% of cases.The median PFS and OS ranged from 3.9 and 13.2 months to 13.7 and 22.3 months, respectively.Again, as different treatment regimens have been applied in these studies, it is more complex to draw definite conclusions.Most studies reported longer survival rates with the proposed interventions than the standard treatment in actual settings.
Nevertheless, the most effective and less toxic regimens include TMZ and BEV, administered together or alone.Based on the last 2 studies, neoadjuvant pre-radiation chemotherapy is most effective when started within the first 2 weeks after surgery.An ongoing large-scale multicenter study called MAGMA is testing the idea of the benefit of neoadjuvant chemotherapy before chemoradiotherapy vs. extended adjuvant therapy in newly diagnosed GBM. 73he results of this study help provide a clearer picture of neoadjuvant chemotherapy.

Conclusions and Future Perspectives
In this review article, most studies on neoadjuvant treatment for newly diagnosed GBM were reviewed.Although in the latest WHO classification (2021) for brain tumors, IDH-wildtype astrocytoma (formerly classified as a lower grade diffuse glioma) is molecularly and prognostically considered in the same category as GBM, this subgroup was not included in the current review.Given that most previous studies have not outlined the IDH mutation status, it is impossible to evaluate the outcomes from other HGG and reach a definite conclusion. 74In some of these studies, no effective neoadjuvant treatment including preoperative CRT was used for GBM.Some studies did not perform surgery, which is the cornerstone of GBM management; some only prescribed postoperative chemotherapy before standard adjuvant CRT, and others only used chemotherapy before surgery.Also, the only de facto preoperative CRT trial has not been published yet (PARADIGMA Trial ClinicalTrials.govIdentifier: NCT03480867).Despite these pitfalls in examining neoadjuvant regimens, promising results have been identified.It is possible to draw 2 conclusions.First, the most frequently used chemotherapy regimen was TMZ plus bevacizumab, which had a promising impact on the outcomes.The merits should be evaluated in a welldesigned study for further conclusions.Second, completion of RT had a significant impact on survival.It should be noted that most patients in these trials were not eligible for the standard multimodality treatment, as some had morbidities that prevented surgery, others a low KPS, and extensive unresectable tumors.

Nabian et al.: State of the neoadjuvant therapy for GBM
Considering the improvements in radiomics, radiogenomics, and liquid biopsy for unresectable or borderline resectable gliomas, more robust recommendations can be proposed regarding selecting candidates for NAT.We suggest exploring the use of CRT with a standard dose of TMZ in the forthcoming trials, besides standard TMZ-based chemotherapy as a postoperative pre-radiotherapy treatment.To examine the use of preoperative chemotherapy alone, we recommend considering TMZ + bevacizumab for 2-3 months as a viable option.This chemotherapy can be followed by standard CRT for adjuvant treatment of any residual tumors.We suggest testing this approach in future trials to determine its effectiveness.To accurately assess the effects of NAT, following the current standard of administering full-dose MGMT-tailored adjuvant treatment is necessary.
Using targeted agents and immunotherapy could have been more helpful for selected cases.However, a small subgroup of patients may benefit significantly, especially from immune checkpoint inhibitors. 28We suggest a strict patient selection for forthcoming trials involving immunotherapy in primary or recurrent tumors as we learned from other solid tumors that not all patients are well-responders, and toxicity may be high. 79However, ICIs could be combined with OV-based therapies to see if heating the immunogenic environment of GBM could improve the efficacy of ICI.

Table 1 .
Summary of Studies Evaluating the Efficacy of Preoperative Therapy for Patients With Newly Diagnosed GBM

Table 2 .
Summary of Studies Evaluating the Efficacy of Neoadjuvant Chemotherapy Before Chemoradiation for Patients With Unresectable Newly Diagnosed GBM

Table 3 .
Summary of Studies Evaluating the Efficacy of Chemotherapy Following Surgery Before Chemoradiation for Patients With Newly Diagnosed Resectable GBM GTR: gross-total resection; PR: partial response; CR: complete response; SD: stable disease; PD: progressive disease; BEV: bevacizumab; IRI: irinotecan; TMZ: temozolomide; OS: overall survival; PFS: progression-free survival; RR: response rate.