Recurrent Glioblastoma: Where we stand.

Current first-line treatment regimens combine surgical resection and chemoradiation for Glioblastoma that provides a slight increase in overall survival. Age on its own should not be used as an exclusion criterion of glioblastoma multiforme (GBM) treatment, but performance should be factored heavily into the decision-making process for treatment planning. Despite aggressive initial treatment, most patients develop recurrent diseases which can be treated with re-resection, systemic treatment with targeted agents or cytotoxic chemotherapy, reirradiation, or radiosurgery. Research into novel therapies is investigating alternative temozolomide regimens, convection-enhanced delivery, immunotherapy, gene therapy, antiangiogenic agents, poly ADP ribose polymerase inhibitors, or cancer stem cell signaling pathways. Given the aggressive and resilient nature of GBM, continued efforts to better understand GBM pathophysiology are required to discover novel targets for future therapy.

Introduction

Glioblastoma multiforme (GBM) is one of the most aggressive primary brain tumors, with a grim prognosis despite maximal treatment. Advancements in the past decades have not significantly increased the overall survival of patients with this disease. The recurrence of GBM is inevitable, its management often unclear and case dependent. In this report, the authors summarize the current literature regarding the natural history, surveillance algorithms, and treatment options of recurrent GBM. In addition, they provide brief discussions regarding current novel efforts in basic and clinical research. They conclude that although recurrent GBM remains a fatal disease, the literature suggests that a subset of patients may benefit from maximal treatment efforts.

Glioblastoma multiforme is a World Health Organization Grade IV tumor that represents 15–20% of all primary intracranial tumors.[1] It is the most malignant astrocytic tumor, with histopathological features that include cellular polymorphism, brisk mitotic activity, microvascular proliferation, and necrosis. The current standard of care for patients with newly diagnosed glioblastoma was established in 2005, following the pivotal trial by the European Organization for the Research and Treatment of Cancer/National Cancer Institute of Canada Clinical Trials Group, in which concurrent temozolomide (TMZ) (75 mg/m2 /d for ≤7 weeks) and radiotherapy followed by 6 maintenance cycles of adjuvant chemotherapy (150–200 mg/m2 on 5-d therapy every 28 d) improved progression-free survival (PFS) and OS.[2]

Despite advances in imaging techniques and multi-modal treatment options, the overall prognosis of patients with GBM remains grim. The median duration of patient survival is estimated to be between 12 and 18 months with maximal treatment, but those without any intervention die soon after diagnosis.[34] So far, very few cases of curative outcome or long-term survival have been reported.[567] In a large retrospective study, Scott et al.,[6] estimated that 2.2% of the cohort survived for >2 years. Overall, the 5-year survival rate is <10%, with a final mortality rate of close to 100%.[89] Glioblastoma has an unfavorable prognosis mainly due to its high propensity for tumor recurrence. It has been suggested that GBM recurrence is inevitable after a median survival time of 32–36 weeks.[1011] The natural history of recurrent GBM, however, is largely undefined for the following reasons: (1) Lack of uniform definition and criteria for tumor recurrence; (2) institutional variability in treatment philosophy; and (3) the heterogeneous nature of the disease, including location of recurrence and distinct mechanisms believed to contribute to known subtypes of GBM.

The criteria used to define recurrent GBM remain ambiguous due to the varied presentation of new lesions. First, the infiltrative nature of GBM cells makes it difficult to eliminate microscopic disease despite macroscopic gross-total resection. Studies have shown that GBM recurrence most often occurs in the form of a local continuous growth within 2–3 cm from the border of the original lesion.[121314] Choucair et al.,[15] reported that more than 90% of patients with glioma showed recurrence at the original tumor location and that multiple lesions developed in 5% after treatment. Second, although less common, GBM may also recur through the development of new parenchymal lesions that fail to exhibit continuous growth patterns, intraventricular spread, or dissemination.[12] Baumann et al.,[16] have shown that uncommon relapse patterns are more prevalent in midline tumors and tumors that infiltrate both hemispheres. Finally, in an attempt to preserve neurological function and maintain patient QOL, subtotal resections are sometimes performed when tumors infiltrate eloquent areas of the brain. Tumor recurrence is also defined by the appearance of residual tumor growth on imaging studies or the manifestation of new clinical symptoms. The term “tumor recurrence” is frequently used synonymously with “tumor progression” because of the spectrum from which new lesions can develop.

Diagnosis of Progression

Serial neuroimaging remains the primary monitoring tool for glioblastoma. Standard magnetic resonance imaging (MRI) contrast studies though beneficial for monitoring, may be misleading and confounding the recurrence even strictly adhered to Mcdonald criteria[17] in first couple of months it becomes difficult to differentiate recurrence from pseudoprogression using T2-weighted, T1-weighted gadolinium, fluid-attenuated inversion-recovery (FLAIR)[18] sequence of MRI. Pseudo progression is featured in 20–30% patient treated with concurrent radiation cum TMZ followed by adjuvant TMZ.[1920] Radionecrosis also appears earlier in patients received chemoradiation than radiotherapy alone.[20] Both pseudoprogression and radionecrosis are likely related to increased tumor cell killing or enhanced host normal tissue reaction. Nonetheless, the recurrence of this type of tumor is purely local.[2122] It is thus advocated to do reimaging in case of suspected pseudoprogression with no rapid change in treatment with no or minimal new symptoms. The first scan after radio chemotherapy should be considered as a new baseline for all further imaging assessment.

A complete resolution of blood brain disturbance detected by contrast extravasation on MRI or computed tomography will no longer qualify as a response if there is increased T2-weighted or FLAIR abnormality and such responses are now termed as “pseudoresponses.” The new Response Assessment in Neuro-Oncology (RANO) criteria integrates a qualitative measure for T2-weighted/FLAIR changes and appears to be an improvement over Mcdonald criteria to interpret the outcome. These criteria are likely to be more valuable in daily practice and clinical trial set up with further validation [Table 1].

Table 1

Neuroimaging and glioblastoma: Macdonald versus RANO criteria

Role of Repeat Surgery and Radiotherapy

A more favorable prognosis following surgery for recurrence or progression is associated with younger age, smaller tumor volume (~50%), motor speech-middle cerebral artery scoring and preoperative Karnofsky performance score (KPS) >80%.[2324] Repeat surgery is not recommended for patients with the involvement of critical structures. Controversial practice sustains with implantation of biodegradable chemotherapy wafers containing carmustine.[25] Nieder et al.[26] found that median survival on re-resection ranged from 14 to 50 weeks, though the role of re-resection by itself remains unclear because most patients receive postoperative chemoradiotherapy.

Reirradiation remains a palliative option for few patients. Patients with KPS more than 60%, tumor size up to 40 mm and progression more than 6 months of the time of surgery appear to be the best candidates.[27] The most common approach could be precision radiotherapy with a total median dose 30–36 Gy.[28] Median survival after various methods of re-irradiation was 26–30 weeks. In a recent review of more than 300 patients, palliative re-irradiation achieved PFS6 of 28–39% and 1-year survival of 18–48%, which compares favorably with systemic targeted therapy for recurrent GBM.[29303132]

Hypofractionated stereotactic radiotherapy is able to deliver treatment over a short course of time, using daily fraction of 3.5 Gy with a median dose of 35 Gy investigators achieved a median survival time of 11 months comparable with other systemic agents in a retrospective study of 147 patients from 1994 to 2008.[33] An analysis of 20 patients with recurrent GBM was designed to test the safety and efficacy of hypofractionated radiotherapy in combination with bevacizumab treatment.[34] The PFS6 was 65% with GBM patients, and median OS was 12.5 months, this result suggests that this combination may be further evaluated in the treatment of both newly diagnosed and recurrent glioblastoma.

A recent retrospective review analyzed 26 consecutive patients who underwent gamma knife radiosurgery for small recurrent high-grade glioma after radical resection, external-beam radiation therapy, TMZ between 2004 and 2009. Median OS was 12.9 months,[35] which was comparable to prospective cohort of 114 patients published by Kong et al.[36]

The most likely reason why radiotherapy is unable to control long-term disease is the inability to detect the spread pattern of GBM.[37] An area of significant interest is the use of systemic radiosensitizers that may enhance the effect of local radiation as well as exert cytotoxic activity on distal cell population.[38]

Monotherapy and Combination Chemotherapeutic Trials for Recurrent Disease

The objective of the analysis was to identify clinical efficacy trials following systemic treatment with nitrosoureas, TMZ, bevacizumab, and/or combinations of these agents in patients with recurrent or progressive glioblastoma. This report is a systematic review that used PubMed and American Society of Clinical Oncology abstract reports from 2006 to 2013 as the primary sources of data.

Nitrosoureas – Single and Combination Therapy

Two phase II trials[3940] and 1 retrospective series[41] evaluated a similar carmustine monotherapy regimen for recurrent/progressive disease in 104 patients, some of whom had received prior TMZ therapy. For 2 studies, PFS6 and median OS ranged 13.0–17.5% and 5.1–7.5 months, respectively; no complete remissions were observed.[2425] Efficacy end points for the one study were unevaluable (data not presented separately for carmustine).[39] The predominant side effects following carmustine monotherapy were hematologic and long-lasting hepatic and pulmonary toxicity [Table 2].

Table 2

Nitrosourea trials in recurrent or progressive glioblastoma

A recent prospective phase III trial in 92 lomustine treated patients (70 at first relapse) reported a 19% PFS6 response rate, with a median OS of 7.1 months.[42] In a double-blind, randomized, multicenter phase III trial of 325 patients who received prior radiation and TMZ, the lomustine monotherapy arm (n ¼ 65) provided PFS6 and median OS of 24.5% and 9.8 months.[4331]

Fotemustine is another nitrosourea compound, studied mostly in Europe, notably in Italy and France.[44] Four prospective phase II trials, using slightly different induction/maintenance dosage regimens, evaluated fotemustine in TMZ-pretreated patients with recurrent or progressive glioblastoma.[45464748] Two studies were exclusively in patients experiencing their first relapse.[4547] Overall, PFS6 and median OS ranged 20.9–61% and 6.0–11.1 months, respectively. Grades 3 and 4 hematologic toxicities were commonly reported following fotemustine therapy; however, lower rates were observed.[45]

Significant hematologic-toxicity concerns and the availability of more effective agents have made the use of nitrosoureas overall less desirable. New schedules at lower doses may prove beneficial. The nitrosoureas seem comparable in terms of efficacy at clinically tolerated doses, whereas nonhematologic toxicity, notably lung fibrosis, may be more common with carmustine than with lomustine or nimustine.

Temozolomide Monotherapy Rechallenge

Six studies of TMZ-pretreated patients evaluated TMZ rechallenge.[495051525354] A variety of metronomic schedules were employed, including 40–100 mg/m2 daily doses given for 21–365 consecutive days, as well as alternating 1-week-on/1-week-off regimens. Overall, PFS6 and median OS ranged 23–58.3% and 5.1–13 months, respectively. One retrospective analysis compiled data on 5 different TMZ dosing regimens among 47 patients (re) challenged while receiving adjuvant TMZ or after a TMZ-free interval.[55] Table 3 PFS6 is 26.3-28.6% for patients progressing on TMZ versus after TMZ; corresponding median OS is 6.6 and 5.3 months, respectively.

Table 3

TMZ monotherapy trials in recurrent or progressive glioblastoma

Of importance in recurrent GBM treatment consideration is the expression of the O6-methylguanine-DNA methyltransferase (MGMT) promoter, which confers resistance to TMZ.[5657] The large multi-center phase II Canadian (RESCUE) study use a continuous dose intense TMZ regimen of 50 mg/m2 /day[58] in patients who had previous exposure to TMZ. This dosing represented dose intensification from 750 to 1000 mg/m2 /28 days cycle with conventional dosing to 1400 mg/m2 /28 days cycle. The overall PFS6 for patients with GBM was 23.9%, and median survival was 9.3 months. The most significant benefit was shown in patients who had completed a previous course of concomitant TMZ/radiotherapy with adjuvant TMZ followed by a draft free period of at least 2 months (PFS6 35.7%). The patients who progressed while still on extended adjuvant TMZ therapy beyond 6 cycles did significantly worse (PFS6 7.4%), but who progressed before completing 6 cycles of adjuvant TMZ had better response (PFS6 27.3%). The investigators hypothesized that a continuous regimen might lead to a depletion of MGMT and restoration of TMZ (Temozolomide) sensitivity as had been previously reported.[59] In addition, the median time from the end of radiotherapy in this early group was 5.2 months, thus minimizing the influence of pseudoprogression on these results.

Three randomized clinical trials were conducted using single-agent TMZ.[605561] In one study, a standard TMZ regimen was more efficacious than procarbazine (PFS6 ¼ 21% vs. 8%), with a median survival time 1.5 months longer.[60] The latter study was conducted in TMZ-naive patients and led to the approval of TMZ in Europe for recurrent glioblastoma, although it is still not approved in the United States. The BR12 study did not provide separate data for glioblastoma patients but indicated that TMZ dose-intense regimens do not provide a survival or PFS benefit compared with standard doses in the treatment of TMZ-naive patients. The DIRECTOR trial evaluated 2 dose-intense regimens of TMZ (120 mg/m2 /d 1-week on/1-week off vs. 80 mg/m2 /d 3 weeks on/1-week off) in patients experiencing a first relapse after at least 2 cycles of TMZ.[53] Specifically, patients were enrolled based on the first progression of glioblastoma documented by MRI no earlier than 180 days after the first surgery and no earlier than 90 days after completion of radiotherapy.

Bevacizumab Monotherapy Trials

Bevacizumab is a human recombinant monoclonal antibody to vascular endothelial growth factor (VEGF), was approved in 2009 by the Food and Drug Administration in the United States for the treatment of recurrent glioblastoma based on response rate;[6263] but not in the European Union. The rejection in Europe was based on the absence of a randomized trial with a bevacizumab-free control arm. In a phase II trial of 35 patients with GBM, Vredenburgh et al.[64] found PFS6 with Bivacizumab + Irinotecan was 46%, and OS6 was 77%. In another phaseII trial, evaluating the role of Bivacizumab alone or in combination with Irinotecan, the PFS6 was 42.6% and 50.3%, respectively.[65] Secondary end points showed OS of 9.2 months with single agent Bivacizumab and 8.7 months for those treated with combination with Irinotecan. The study did show a trend for decreasing steroid dose in patients on therapy.

A recent meta-analysis comprising fifteen studies published between 2005 and 2009,[66] on recurrent GBM showed median OS, PFS6 and OS6 were 9.3 months, 45%, and 76% respectively. The analysis found no difference in Bivacizumab dose response benefit between 5, 10 and 15 mg/kg. A retrospective study of 161 patients with recurrent GBM treated with Bivacizumab found an incidence of 1.9% and 1.9% for ischemic stroke and intracranial bleeding respectively.[67] Prolonged anti angiogenic therapy may produce ischemic stroke whereas intratumoral bleed may be caused from tumor progression. Despite its efficacy in recurrent GBM, patients inevitably relapse and patients progressing on one Bivacizumab containing regime respond poorly on alternative Bivacizumab containing regime.[68]

Meanwhile, data from 2 large randomized trials, AVAglio and Radiation Therapy Oncology Group 0825, adding Bevacizumab to TMZ chemoirradiation, are likely to shape the future standards of care both at diagnosis and at recurrence.

Other Anti-angiogenic Agents

The VEGF receptor (VEGFR) inhibitor cediranib was explored in patients with recurrent glioblastoma in a very sophisticated fashion using advanced neuroimaging and biomarker studies.[6970] PFS6 of 31 patients with recurrent glioblastoma treated with cediranib monotherapy at a starting dose of 45 mg/d was 25.8%. Response rates were 56.7% for three-dimensional measurements and 27% for two-dimensional measurements. Toxicities were moderate.

Aflibercept (VEGF trap) that inhibits both VEGF and placental growth factor, was administered to 42 patients with recurrent glioblastoma at first relapse.[71] Efficacy of VEGF trap as a single agent for recurrent disease was minimal, with PFS6 of 7.7%, although 2 patients had durable response (alive at 150 weeks). XL184, an inhibitor of MET, VEGFR2, and RET, was given p.o. (125 mg/d or 175 mg/d) to 124 patients with recurrent glioblastoma.[72] Overall, interim PFS6 for the 125-mg and 175-mg groups were 25% and 21%, respectively.[73] Cilengitide, an inhibitor of avb3 and avb5 integrin receptors, showed modest single-agent activity that is, PFS6 of 15% and median OS of 9.9 months, following a 2000-mg twice-daily continuous regimen among 40 patients with recurrent glioblastoma.[74]

Angiogenesis is also regulated by integrin-mediated signaling. Integrins, cell-surface adhesion molecules that are often overexpressed in gliomas, mediate cell adhesion, migration and invasion into the surrounding tissue. Agents that target integrins, such as EMD121974 (cilengitide), found to be active when combined with TMZ and RT in newly diagnosed GBM patients,[75] were evaluated as a single agent in a Phase IIa trial in patients with recurrent GBM; the toxicity profile was manageable, no cases of grade 4 toxicity occurred and the PFS-6 was 15%.[76]

Temozolomide - Containing Combination

During last decade, a number of studies have investigated the efficacy and safety of TMZ in combination with VEGF, Nitrosoureas, interferon, as well as plenty of other conventional chemotherapeutic agents for recurrent GBM. Desjardins et al.[77] evaluated the combination of protracted TMZ (50 mg/m2 /d) and Bevacizumab (10 mg/kg intravenous [i.v.] every 2 weeks) in 32 TMZ pretreated patients who predominantly were experiencing a first or second recurrence (94%). A radiographic response was observed in 9/32 patients. PFS6 was 18.8% with a median OS of 8.7 months. MGMT status did not appear to be related to the outcome.

A protracted daily TMZ and sorafenib regimen had very limited activity, despite a good safety profile, in 32 patients with recurrent disease.[78] PFS6 was very low (9.4%). The poor results may be attributed to heavy pretreatment, higher failure rate to previous Bevacizumab therapy, lack of selection of patients with sorafenib target expression, and the relatively high use of CYP3Ainducing antiepileptic drugs that may have compromised sorafenib activity.

The combination of TMZ and afatinib (40 mg/d), an irreversible blocker of the epidermal growth factor receptor (EGFR), was investigated in a phase II study.[79] PFS6 was 10% for the combination compared with 3% for afatinib alone (P ¼.008) and 23% for TMZ alone (P ¼.59).

A retrospective study of 28 patients found that the combination of continuous low-dose TMZ (10 mg/m2 b.i.d.) and celecoxib (200 mg/d) had some activity in treating recurrent glioblastoma without significant toxicity.[78] The majority of patients (86%) were being treated for their first recurrence. PFS6 was 43%. MGMT promoter methylation did not predict a favorable outcome.

Gaviani et al.[80] evaluated the combination of TMZ and fotemustine in 10 patients with recurrent disease following chemoradiation. The study was terminated early (planned enrollment of 105) because of severe hematologic toxicities.

Overall, the TMZ combination studies available to date do not suggest that one particular chemotherapy combination regimen is more effective than administration of TMZ alone.

Bevacizumab-Containing Combination

In theory, the combination of Irinotecan and Bevacizumab might improve efficacy owing to a synergy of antiangiogenic and cytostatic properties. Six studies in 357 evaluable patients, including 1 retrospective analysis, evaluated Bevacizumab in combination with irinotecan.[818283846685] Overall PFS6 was 30.0–50.3% with median OS of 6.1–9.7 months. Overall, no additional benefit of Irinotecan over Bevacizumab alone became apparent. The addition of cetuximab was relatively well tolerated, except for skin toxicity; however, overall efficacy did not appear to be enhanced with the addition of Cetuximab to the Bevacizumab + Irinotecan combination regimen.

Reardon et al.[86] evaluated the efficacy of Bevacizumab and Eoposide among 27 patients with primarily first recurrences. Complete and partial response was observed in 1 and 6 patients, respectively. PFS6 of 44.4% and median OS of 10.2 months were reported. Notably, high VEGF expression was associated with a better PFS.

Sathornsumetee et al.[87] evaluated bevacizumab in combination with erlotinib, an EGFR tyrosine kinase inhibitor. PFS6 and median OS were 29.2% and 10.3 months, respectively. Survival end points of patients treated more than 3 months postradiotherapy were similar to those of the overall population. In summary, this combination did not appear to provide improved survival benefits compared with historical bevacizumab-containing regimens.

Targeted Therapies

Recent advances in the understanding of molecular and cytogenetic pathways that influence tumor growth, invasion, angiogenesis, and apoptosis have led to the direct targeting of the aberrant pathways found in cancer. Treatments against specific molecular targets, in particular, the EGFR, have been investigated in brain tumor patients. EGFR amplification and overexpression, present in approximately 50% of GBM patients, are associated with a poor prognosis. In recent years, small-molecule inhibitors targeting tyrosine kinases, such as erlotinib and gefitinib have been widely evaluated in neuro-oncology.

In Phase II gefitinib trial on a series of 53 patients with recurrent GBM, no objective responses were found.[68] The PFS-6 (13%) was the same as in historical controls, with other agents considered inactive. In this trial, EGFR protein expression and gene status, and EGFRvIII protein expression were not significantly correlated with PFS-6 and survival, and gefitinib as a single agent was considered inactive in this setting. Haas-Kogan et al. observed that the response to erlotinib treatment was greater in GBM patients with high EGFR expression and low phospho-Akt levels than in those with low EGFR expression and high phospho-Akt levels. The authors found no correlation between EGFRvIII expression and response.[88] In their study on 49 GBM patients treated with erlotinib or gefitinib, Mellinghoff et al. found that EGFRvIII and PTEN protein co-expression was correlated with the response to treatment.[89] More recently, a large and well-conducted randomized Phase II study of the EORTC 26034 trial compared first-line erlotinib with either TMZ or BCNU as standard treatments[90] and found that results were disappointing when the EGFR inhibitor was given as a single agent for recurrent disease: PFS-6 was 12% in the erlotinib arm and 24% in the control arm. Furthermore, a Phase II trial of erlotinib in combination with carboplatin showed that the activity of this regimen was modest, with the PFS-6 being 14%. In addition, no correlation was observed between EGFR, Akt or PTEN expression, and PFS or OS.[91] Other targeted therapies have been investigated in the neuro-oncological setting Table 2. In addition, a small exploratory study on[16] F-fluorothymidine PET in malignant glioma patients treated with Bevacizumab and Irinotecan showed that metabolic response was predictive of OS while MRI radiological response showed only a trend, and that metabolic responders did not clearly correlate with PFS, confirming that classical neuroradiological imaging should not provide conclusive information about the activity of this regimen.[92]

A significant percentage of GBMs have PTEN gene suppression alterations, resulting in the increased activation of the downstream PI3K/Akt/mTOR pathway, which regulates cell survival and proliferation; the deregulation of this pathway is thought to play a role in tumor pathogenesis. Thus, another target for new compounds is mTOR, a serine/threonine kinase that acts as a central component of the PI3K/Akt signaling pathway that mediates cell growth and proliferation. Efforts to downregulate this pathway have been pursued through inhibitors of mTOR, such as rapamycin (sirolimus), RAD-001 (everolimus) and CCI-779 (temsirolimus). Two recently completed trials on temsirolimus in patients with recurrent GBM report a PFS-6 of 2.5 and 7.8%, respectively [Table 4].

Table 4

Results of phase II trials of small molecule-targeted therapies

Finally, imatinib mesylate, a small-molecule inhibitor of KIT, Bcr/Abl and PDGF receptor (PDGFR), has been evaluated in recurrent gliomas in a multicenter EORTC Phase II trial. In patients with recurrent GBM, PFS-6 was 16%, and overall PFS was not correlated with PDGFR-a single nucleotide polymorphisms.[41]

Another promising treatment modality lies in immunotherapy. Early-stage immunotherapeutic treatments can be divided into two major categories: Targeted toxin therapy and anticancer vaccinations.[93] These two mechanisms use separate aspects of human immune response to targeted toxins or T cells, which are directed toward tumoral remnants. Authors of one study examined the effects of lymphokine-activated killer-cell implantation on recurrent GBMs. Of 40 patients in whom recurrent GBM was diagnosed, a median survival of 9 months and a 1-year survival rate of 34% were achieved.[94] Techniques involving gene therapy are producing comparable results. In a small study in which the authors examined the effects of an intratumoral injection of retroviral vector–producing cells combined with i.v. ganciclovir, they noted a 1-year patient survival rate of 25% with tumor response in 50% of the cases.[95] The future role of immunotherapy and gene therapies will become clearer as more Phase I and II clinical trials are completed. However, current experimental applications may provide a case-specific increase in survival time.

Standard of Care Recommendations for Recurrent Glioblastoma

Appropriate management outside of clinical trials requires individualization based on patient age, performance status, histology, extent of initial resection, type of and response to initial therapy, time since diagnosis, and whether the recurrence is local or diffuse. Repeat surgery, reirradiation, and second-line mono or combination therapy are all directed primarily at reducing tumor burden and extension. All therapies aim to improve neurologic symptoms, such as headaches or seizures; reduce the need for certain medications or lower total daily doses, e.g., corticosteroids or antiepileptic drugs; and prevent thromboembolic complications.

Currently, limited evidence exists from randomized studies to explain the variable nature of the recurrent GBM and differences among institutional first-line treatment. Among patients determined to be favorable surgical candidates (those with high KPS scores, noneloquent location, and no medical contraindications), the addition of BCNU wafers appears to provide additional benefits. Regarding the administration of chemotherapy, either as the primary or an adjunctive therapy, the potential benefits appear to be independent of the number of agents used. Currently, TMZ is rapidly becoming the standard chemotherapy agent due to its ease of administration, minimal side-effect profile, and established improvement in survival rates.

Repeated resection should be considered in patients with high preoperative KPS scores or in those whose symptoms are secondary to mass effect from superficial noneloquent regions. The benefits of stereotactic radiosurgery and chemotherapy are similar and should be chosen based on their corresponding side-effect profiles. In general, improved outcomes are witnessed with combined radiotherapy and chemotherapy compared with each treatment alone.

Current trends indicate that the treatment of recurrent GBM will remain multimodal in nature. Further understanding of underlying tumor biology is essential in developing more effective strategies. Research in gene therapy, antiangiogenic antagonists, and immunotherapies holds great promise. With continual improvements in treatments and imaging techniques, it is the hope of clinicians, researchers, and patients that GBM may become a controllable disease with a favorable prognosis.

Conclusions

A plethora of monotherapy and combination chemotherapy strategies have been evaluated in patients with recurrent glioblastoma. Despite some minor improvements in PFS, no obvious increase in survival has been associated with any particular regimen. Future clinical trials that adopt the revised Macdonald criteria (RANO) may provide new clues as to which agent or combination is most beneficial. Despite definitive data, the standard of care guidance for managing patients with recurrent glioblastoma is evolving. However, the development of novel therapeutic options for patients with recurrent GBM remains a priority. The results to date for anti-angiogenic treatments appear promising but definitive results are needed. Other agents currently in clinical development for recurrent GBM include new molecular targeted therapies; whenever possible, patients should be given the opportunity to participate in experimental trials.