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Keywords:

  • low-grade glioma;
  • astrocytoma;
  • IDH1;
  • TP53;
  • MGMT;
  • outcome;
  • prognostic factor

Abstract

  1. Top of page
  2. Abstract
  3. MATERIALS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. FUNDING SOURCES
  7. REFERENCES

BACKGROUND:

The favorable prognostic impact of mutations in the IDH1 gene is well documented for malignant gliomas; its influence on World Health Organization (WHO) grade II astrocytomas, however, is still under debate.

METHODS:

A previously published database of 127 predominantly surgically treated patients harboring WHO grade II astrocytomas was revisited. Patients were screened for TP53 mutations (sequencing analysis), IDH1 mutations (pyrosequencing), and MGMT promoter methylation (methylation-specific polymerase chain reaction and bisulfite sequencing). Endpoints were overall survival, progression-free survival (PFS), time to malignant transformation, and postrecurrence survival. Radiotherapy was usually withheld until tumor progression/malignant transformation occurred.

RESULTS:

IDH1 mutations, TP53 mutations, and methylated MGMT promoters were seen in 78.1%, 51.2%, and 80.0% of the analyzed tumors, respectively. IDH1 mutations, which were significantly associated with TP53 mutations and/or MGMT promoter methylation (P < .001), resulted in shortened PFS (median, 47 vs 84 months; P = .004); postrecurrence survival, however, was significantly increased in those patients undergoing malignant transformation (median, 49 vs 13.5 months; P = .006). Overall survival was not affected by IDH1. A similar pattern of influence was seen for MGMT promoter methylation. Methylated tumors did significantly worse (better) in terms of PFS (postrecurrence survival); a low number of unmethylated tumors, however, limited the power of this analysis. Conversely, TP53 mutations were stringently associated with a worse prognosis throughout the course of the disease.

CONCLUSIONS:

IDH1 mutations are associated with a Janus headlike phenomenon; unfavorable prognostic influence on PFS turns into favorable impact on postrecurrence survival. A similar pattern of influence might exist for MGMT methylation. Cancer 2011;. © 2011 American Cancer Society.

Molecular biomarkers such as 1p19q codeletion, O6-methylguanine DNA methyltransferase (MGMT) promoter methylation, and TP53 and isocitrate dehydrogenase 1 (IDH1) mutational status have contributed to a more objective classification of gliomas and are increasingly used for prognostic/predictive modeling and stratification into molecularly determined treatment groups.1-3 The family of IDHs comprises enzymes that catalyze oxidative decarboxylation of isocitrate into α-ketoglutarate by using nicotinamide adenine dinucleotide (NAD) or NAD phosphate (NADP) as a cofactor.4 Heterozygous IDH1 mutations frequently occur in gliomas5-7 and inhibit wild-type IDH1 enzymatic activity for its substrate through the formation of catalytically inactive heterodimers. Instead, mutated IDH1 gains the ability to reduce α-ketoglutarate to D(-)-2-hydroxyglutarate.8 The accumulation of this metabolite has been shown to be associated with tumor progression and an increased risk of malignant gliomas.8 Furthermore, presumably resulting from suppressed prolyl hydroxylase activities, expression of mutant IDH1 is associated with increased intracellular level and transcriptional activity of hypoxia inducible factor 1α,9, 10 a component of the hypoxia-responsive transcription factor complex that has been involved in angiogenesis and tumor growth.11 IDH1 mutations are very frequent in World Health Organization (WHO) grade II astrocytomas (∼80%), anaplastic astrocytomas WHO grade III (64%), low grade/anaplastic oligotumors (66%-80%), and secondary glioblastomas (83%).6, 12-14 IDH2 mutations are rare.6 Whereas the favorable impact of IDH1 mutations on outcome scores is well documented for WHO grade III and grade IV gliomas,5, 14-16 their impact on grade II gliomas is still under debate. Available studies, mainly dealing with oligodendrogliomas and oligoastrocytomas, have found significantly longer survival times in IDH1-mutated tumors.15, 17 Conversely, in a recently published study, which has included a large group of both astrocytomas and oligotumors, no influence of IDH1 mutations on length of survival was detected; this study pointed to the strong unfavorable influence of TP53 mutations in astrocytomas and the favorable impact of a 1p/19q codeletion in oligotumors.2 However, no detailed outcome data (in terms of progression-free survival [PFS] and postrecurrence survival) were given in this report.

In the current long-term analysis, exclusively WHO grade II astrocytomas were addressed. Surprisingly, IDH1 mutations were associated with a Janus headlike phenomenon. We showed that IDH1 mutations were associated with a significantly shorter PFS after open tumor resection. Conversely, postrecurrence survival was significantly longer for those patients undergoing malignant transformation simultaneously with tumor progression or later; most of these patients were treated with delayed radiotherapy at the time of malignant transformation. A similar pattern of influence was also seen for MGMT promoter hypermethylation.

MATERIALS AND METHODS

  1. Top of page
  2. Abstract
  3. MATERIALS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. FUNDING SOURCES
  7. REFERENCES

Inclusion Parameters, Treatment Protocol, and Patient Follow-up

A previously published database dealing with the prognostic role of TP53 mutations in adult patients with supratentorial WHO grade II gliomas (159 patients) was revisited.18 Exclusively patients harboring WHO grade II astrocytoma (overall N = 128) were considered eligible for this study. Patients with oligoastrocytomas (n = 24), those with undefined low-grade glioma subtypes (n = 7), and those lost to follow-up (1 patient) were excluded, leaving 127 patients in the current analysis. All of the tumor specimens were centrally histologically reviewed at the German National Brain Tumor Reference Center (Bonn, Germany) in accordance with the WHO 2000 classification system, as has been described previously19; histological evaluation was not updated for the current analysis. Patients were consecutively enrolled and treated between January 1991 and December 1998 at the Department of Neurosurgery, Grosshadern Clinical Center, Ludwig Maximilians University (Munich, Germany). In 25 patients, however, first tumor resection was done before 1991 at other neurosurgical departments. Last follow-up was performed in August 2010. Patients' demographic data are summarized in Table 1. Written informed consent for molecular genetic analysis was obtained from all patients at the time of study enrollment. Microsurgical resection was the most commonly used treatment method. For 21 patients with surgically inaccessible tumors, however, stereotactic biopsy (BX) was performed to establish histopathological diagnosis. Extent of resection was determined on the basis of the intraoperative opinion of the surgeon and/or on the basis of any relevant description in the surgical records. Stereotactic brachytherapy was used as first-line treatment in selected patients with small (diameter ≤4 cm), circumscribed, and eloquently located gliomas not accessible for open tumor resection. Conventionally fractionated limited field radiotherapy (tumor dose, 50-60 grays) was generally applied as second-line treatment for patients with documented tumor progression (not accessible for surgical retreatment) and those undergoing malignant transformation. Chemotherapy was used as third-line treatment for selected patients in case of tumor progression after radiotherapy. Follow-up included clinical and neuroradiological magnetic resonance imaging (MRI) evaluation at 6-month intervals until the time of the last examination.20 Tumor progression was defined as an unequivocal increase in tumor size on follow-up T2-weighted MRI. Malignant transformation was considered to have occurred when 1) grade III/IV disease was histologically diagnosed after resurgery or biopsy or 2) when multilocular tumor appearance and/or contrast enhancement on an initially nonenhancing lesion was observed in combination with rapid tumor growth.

Table 1. Patient Demographics and Clinical Characteristics
VariableOverall, 127 Patients
  1. Abbreviations: BX, biopsy; F, female; GTR, gross total resection; IDH1, isocitrate dehydrogenase 1; KPS, Karnofsky performance score; M, male; MGMT, O6-methylguanine DNA methyltransferase; STR, subtotal resection.

Age, y, median [range]37.0 [18.0-75.0]
 <50103
 >5024
Sex, M/F60/67
KPS, median [range]80 [50-100]
Histology 
 Fibrillary astrocytoma118
 Gemistozytic astrocytoma8
 Protoplasmatic astrocytoma1
Surgery 
 GTR58 (45.7%)
 STR48 (37.8%)
 BX21 (16.5%)
IDH1 R132 mutations89/114 (78.1%)
TP53 mutations65/127 (51.2%)
MGMT promoter methylation36/45 (80.0%)

Molecular Genetic Analysis

IDH1, TP53, and MGMT analyses were performed using DNA that was either directly isolated from fresh tissue samples harvested from open tumor resection and immediately frozen at −80° or extracted from paraffin-embedded tissues. DNA quantity and quality were routinely checked using the ND-1000 spectrophotometer as well as 0.8% agarose gels. Overall amount of DNA did not allow loss of heterozygosity analysis on chromosomes 1p and 19q in our study.

Detection of IDH1 Mutations

IDH1 mutation were examined by pyrosequencing. Primer design for IDH1 was performed with PSQ Assay design Software (Qiagen, Hilden, Germany) based on accession numbers NC_000002.11 (209100953-209119806). A fragment of 88-bp length including codon 132 was amplified using the forward primer 5′-biotin-AAAAATATCCCCCGGCTTG-3′ and reverse primer 5′-TGCCAACATGACTTAC-TTGATCC-3′. Polymerase chain reaction (PCR) was performed in a 200-μL tube with a final volume of 40 μL using the HotStarTaq DNA Polymerase Master Mix Kit (Qiagen) according to the manufacturer's instructions with 20 ng of DNA. Each PCR was accompanied by a no template control. The initial denaturation (95°C, 15 minutes) was followed by 40 cycles of 20 seconds at 94°C, 20 seconds at 52°C, and 30 seconds at 72°C and a final extension step at 72°C for 5 minutes. The PCR product was checked by gel electrophoreses including no template controls. Then, 10 μL of the PCR product as well as the no template control were subjected to pyrosequencing on a PyroMark Q24 System using the Pyro Gold reagents kit (both by Qiagen) using the sequencing primer 5′-TGATCCCCATAAGCAT-3′. Subsequent purification and processing of the biotinylated single-strand DNA was performed according to the manufacturer's instructions. Resulting data were analyzed and quantified with PyroMark Q24 Software (Qiagen).

Detection of TP53 Mutations and MGMT Promoter Methylation

TP53 gene mutations were screened for exons 5 to 8 by using previously reported primers and methods.21 DNA methylation status of the MGMT promoter was determined by both bisulfite modification and subsequent nested methylation-specific PCR and sequencing analysis using established protocols.22, 23 Definition of MGMT methylated versus unmethylated tumors was in accordance with Grasbon-Frodl et al.22

Statistical Analysis

The reference point of the study was the date of first surgical treatment. Date of last follow-up was August 2010. Study endpoints included death, tumor recurrence or progression, and malignant transformation. Postrecurrence survival was defined as the time interval between tumor recurrence/progression and death/last follow-up. Overall survival (OS), PFS, postrecurrence survival, and time to malignant transformation were analyzed using the Kaplan-Meier method.24 Potential prognostic factors were identified using a proportional hazards model.25 Parameters, which were significant in 1-variable analyses, were included in multivariate models. The optimized model contained only variables that were significantly associated with the endpoint of interest after adjustment for the effects of other variables included in the model. Each optimized model was validated by verifying that no term in the model could be added or omitted without significantly altering the maximized likelihood. Alternative models were compared by computing maximized likelihoods. Dichotomous variables were analyzed with the chi-square statistic and continuously scaled variables with the Wilcoxon test. Median follow-up was calculated from the date of the fist surgical procedure taking into account the respective last observations in surviving cases and censoring nonsurviving cases. Results were considered significant at P < .05. All reported P values are 2 sided. All calculations were performed using the SAS software package (version 9.1; SAS Institute, Cary, NC).

RESULTS

  1. Top of page
  2. Abstract
  3. MATERIALS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. FUNDING SOURCES
  7. REFERENCES

Patient Characteristics

The study comprises 127 adult patients with supratentorial WHO grade II gliomas (Table 1). Median follow-up for the survivors was 173 months (range, 36-306 months). This calculation included 8 patients, for whom follow-up could not be updated in August 2010 (in these patients, follow-up ranged from 36 to 114 months; median, 83 months). Gross total resection, subtotal resection, and BX were performed in 58, 48, and 21 patients, respectively. Seven patients with eloquently located, small, circumscribed tumors underwent stereotactic iodine-125 brachytherapy as primary treatment. Five patients with large residual tumor volumes after open tumor resection and 6 patients who underwent BX were treated with early radiotherapy. Surgical retreatment of tumor recurrences was done in 47 patients. Seventy-eight (61.4%) patients received delayed radiotherapy (74 patients at the time of malignant transformation). Delayed chemotherapy was initiated in 24 (18.9%) patients, usually as third-line treatment. Patients undergoing malignant transformation (n = 80) were more likely to receive external beam radiation and/or chemotherapy than those remaining 26 patients experiencing tumor progression without malignant transformation (P < .001). Evaluation of treatment strategies did not indicate differences with regard to the IDH1 and MGMT methylation status.

TP53 mutations were found in 65 of 127 tumors. For detailed information on the TP53 mutational status see Stander et al18 and Peraud et al.21 The IDH1 mutational status could be determined in 114 of 127 (number of IDH1-mutated tumors: 89) and the MGMT promoter methylation status in 45 of 127 tumors (number of methylated tumors: 36). DNA quality was not sufficient for valid analysis of the remaining tumors. The predominant amino acid sequence alteration in IDH1 was R132H (90% of the detected mutations), followed by R132C (9%). In 1 tumor, alteration in both R132H and R132C were found. Patients with known and unknown IDH1 mutational status and those with known or unknown MGMT promoter methylation status did not differ in terms of age, histology, Karnofsky performance score (KPS), treatment, and outcome measurements (data not shown). The frequency of TP53 and IDH1 mutation and that of MGMT promoter methylation were not influenced by sex, patients' age, or tumor location. The frequency of IDH1 mutations was significantly correlated with the frequency of both a TP53 mutation and MGMT promoter methylation; 97% of the methylated and 94% of the TP53-mutated tumors exhibited an IDH1 mutation (P < .0001). Vice versa, a mutational TP53 status was found in 68.5% of the IDH1-mutated tumors. No significant association was seen between TP53 mutational status and MGMT promoter methylation (P = .1).

Estimates of OS, PFS, and time to malignant transformation were based on 85, 106, and 80 events, respectively; median OS, PFS, time to malignant transformation, and postrecurrence survival were 118 months, 51 months, 100 months, and 45 months, respectively (Table 2). Twenty-five patients treated before 1991 did not significantly differ from those treated at later time points in terms of age, KPS, PFS, time to malignant transformation, and OS (P > .05). Long-term survivors without signs of tumor progression after >100 months follow-up (n = 15) had a significantly lower frequency of both TP53 (20% vs 55%, P = .01) and IDH1 mutations (46% vs 82%, P = .003) than the remaining patients.

Table 2. Clinical Outcome
FactorOverall Population, 127 PatientsIDH1 R132 MutationP
Yes, 89 PatientsNo, 25 Patients
  • Abbreviations: IDH1, isocitrate dehydrogenase 1; n.r., not reached.

  • a

    Statistically significant.

Overall survival, mo    
 Median (range)118 (96-130)112 (87-130)118 (48-n.r.).38
 Rate at 5 years76.0%75.1%71.2% 
 Rate at 10 years47.5%47.3%47.3 % 
Progression-free survival, mo    
 Median (range)51 (41-63)47 (35-60)84 (39-184).004a
 Rate at 5 years44.0%37.8%59.3% 
 Rate at 10 years17.4%10.5%41.4% 
Time to malignant transformation, mo    
 Median (range)100 (74-115)92 (72-119)106 (39-n.r.).289
 Rate at 5 years69.0%67.2%67.8% 
 Rate at 10 years39.4%37.9%44.8% 
Postrecurrence survival, mo    
 Median (range)45 (30-58)49 (36-63)13.5 (4-64).006a
 Rate at 1 year80%87.9%50.0% 
 Rate at 5 years39%40.7%25.7% 

IDH1 Mutations Are Associated With Both Unfavorable PFS and Prolonged Postrecurrence Survival

A summary of outcome data is given in Table 2. Patients with IDH1-mutated tumors did significantly worse in terms of PFS, whereas time to malignant transformation and OS were not influenced by this biomarker (Fig. 1). Five-year (10-year) PFS rates were 59.3 % (41.4%) for wild-type IDH1 tumors and 37.8% (10.5 %) for IDH1-mutated tumors (P = .004). Conversely, postrecurrence survival in those undergoing malignant transformation simultaneously with the onset of tumor progression or later was significantly better for IDH1-mutated tumors (1-year postrecurrence survival rate, 87.9%; median, 49 months vs 50.0%; median, 13.5 months; P = .006; Fig. 2). The exclusive focus on those tumors harboring an unequivocal astrocytic genotype (ie, tumors exhibiting a TP53 mutation alone or in combination with an IDH1 mutation and tumors without IDH1 mutations) revealed a similar pattern of influence of IDH1 regarding PFS, OS, and postrecurrence survival (data not shown).

thumbnail image

Figure 1. Kaplan-Meier estimates show progression-free survival (A, B) and overall survival rates (C, D) of patients with World Health Organization grade II astrocytomas stratified for IDH1 (A, C) and TP53 (B, D) mutational status. Circles indicate censored events.

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thumbnail image

Figure 2. Kaplan-Meier estimates show postrecurrence survival rates stratified for the IDH1 mutational status. Circles indicate censored events.

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The influence of MGMT promoter methylation pointed to a direction similar to that of IDH1; PFS was better for unmethylated tumors (5-year [10-year] PFS rates: 62.5% [50%] vs 39.4% [6%] for methylated tumors); the difference was statistically significant (P < .05). In contrast, postrecurrence survival (for those undergoing malignant transformation) was longer for methylated tumors (1-year postrecurrence survival rate: 86.7%; median, 52 months vs 5%; median, 13 months; P < .01). The power of this analysis, however, was limited by the low number of unmethylated tumors. We were not able to determine the impact of biomarkers on postrecurrence survival for those 26 patients without signs of malignant transformation as a consequence of the small sample size.

TP53 Mutations Indicate Worse Prognosis

TP53 mutated tumors did significantly worse in terms of PFS and OS (Fig. 1); no significant influence was seen on time to malignant transformation and postrecurrence survival. The 5-year (10-year) OS rate for patients without TP53 mutations was 81.8% (56.9%), compared with 70.5% (38.7%) for those exhibiting a mutant TP53 status (P = .01). The corresponding PFS values were 55.4% (25.0%) and 36.5% (10.5%), respectively (P = .01).

Multivariate Models

A compilation of 1-variable and multivariate models for OS, PFS, postrecurrence survival, and time to malignant transformation is shown in Table 3. Whereas a mutated IDH1 status gained predominant unfavorable influence on PFS (P = .005; risk ratio, 2.17; 95% confidence interval, 1.26-3.74) in multivariate models (the univariately detected influence of the TP53 mutational status was lost), OS was not affected by IDH1; instead, increased age (continuously scaled, P = .02; risk ratio, 1.02; 95% confidence interval, 1.00-1.04) and TP53 mutations (P = .02; risk ratio, 1.66; 95% confidence interval, 1.07-2.56) gained unfavorable impact. These results suggested that IDH1-mutated tumors with and without TP53 mutations did not differ in terms of PFS, whereas IDH1-mutated tumors with TP53 mutation did significantly worse in terms of OS, as compared with those without a TP53 mutation. The univariately detected favorable impact of a mutated IDH1 status on postrecurrence survival was also confirmed multivariately (IDH1: P = .01; risk ratio, 0.45; 95% confidence interval, 0.24-0.85) after adjustment for the effects of age. No distinct influence of TP53 mutation on postrecurrence survival could be determined.

Table 3. Univariate and Multivariate Models
CharacteristicP (HR/95% CI)
OSPFSTTMPRS
  • Abbreviations: BX, biopsy; CI, confidence interval; GTR, gross total resection; HR, hazard ratio; IDH1, isocitrate dehydrogenase 1; KPS, Karnofsky performance score; MGMT, O6-methylguanine DNA methyltransferase; OS, overall survival; PFS, progression-free survival; PRS, postrecurrence survival; STR, subtotal resection; TTM, time to malignant transformation.

  • a

    Statistically significant.

Univariate models    
 Increased age, continuously scaled.014a (1.02/1.00-1.04).15 (1.01/1.00-1.03).56 (1.01/0.99-1.02).002a (1.04/1.01-1.06)
 Sex, male vs female.15 (0.73/0.47-1.12).70 (0.93/0.63-1.36).14 (0.72/0.46-1.12).75 (0.93/0.56-1.45)
 KPS at diagnosis, ≥80 vs <80.73 (1.09/0.68-1.74).78 (1.06/0.70-1.62.36 (0.79/0.47-1.3).038 (1.74/1.03-2.95)
 Location, lobar vs deep.66 (1.20/0.52-2.76).47 (0.75/0.35-1.62).45 (1.35/0.62-2.94).32 (1.54/0.66-3.57)
 Surgery, GTR vs STR/BX.32 (1.25/0.81-1.93).63 (1.10/0.075-1.6).89 (1.03/0.66-1.61).07 (1.56/0.96-2.53)
 IDH1, wild type vs mutant.38 (1.30/0.72-2.33).005a (2.17/1.26-3.74).29 (1.37/0.76-2.48).008a (0.43/0.23-0.8)
 TP53, wild type vs mutant.01a (1.72/1.11-2.65).01a (1.64/1.12-2.43).55 (1.14/0.74-1.77).13 (1.47/0.89-2.41)
 MGMT, nonmethylated vs methylated.76 (1.10/0.41-3.40).03 (3.20/1.10-9.10).31 (1.73/0.60-4.98).01 (0.24/0.08-0.78)
Multivariate models    
 Increased age, continuously scaled.02a (1.02/1.00-1.04)  .001a (1.04/1.02-1.07)
 IDH1, wild type vs mutant .005a (2.17/1.26-3.74) .01a (0.45/0.24-0.85)
 TP53, wild type vs mutant.02a (1.66/1.07-2.56)   

DISCUSSION

  1. Top of page
  2. Abstract
  3. MATERIALS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. FUNDING SOURCES
  7. REFERENCES

In glial tumors, mutations in IDH family members frequently occur and are considered early events in gliomagenesis. Whereas the favorable influence of IDH1 mutations in high-grade gliomas has convincingly been demonstrated,5, 6 their influence in WHO grade II astrocytomas is much less clear. Studies that have also claimed a positive influence of IDH1 mutations on length of survival in grade II gliomas have mainly focused on oligodendrogliomas and oligoastrocytomas.15, 17 In a recently published study, which included both grade II astrocytomas and oligotumors, the positive influence of IDH1 mutations on length of survival was surprisingly lost; instead, this study emphasized the unfavorable role of TP53 mutations in astrocytomas and the favorable role of 1p/19q codeletions in oligotumors.2 However, given the finding that 1) most grade II astrocytomas underwent malignant transformation during the course of the disease and 2) favorable prognostic influences of IDH1 mutations on length of survival for secondary malignant gliomas have already been clearly demonstrated,6, 13 one would have expected better survival times for IDH1-mutated tumors. This apparent inconsistency could be explained by the findings of the current study. We demonstrate that IDH1 mutations exhibited both unfavorable and favorable influence at different time points of the disease. Whereas IDH1 mutations were associated with a significantly shortened PFS (after surgical treatment), postrecurrence survival was significantly improved in those patients exhibiting signs of malignant transformation simultaneously with tumor progression or later. Thus, Janus headlike phenomena related to IDH1 mutations explain that this biomarker did not affect length of survival. Similar to IDH1, Janus headlike properties could also be assumed for the MGMT promoter methylation status. Patients with a methylated promoter had shorter PFS in this series; postrecurrence survival, however, was significantly longer, whereas overall survival again was not influenced. Although the power of this analysis was limited by both the small number of unmethylated tumors and the low overall number of tumors with a known methylation status, our findings are in line with those of others. Whereas Komine et al26 have already described a shortened PFS in methylated diffuse low-grade astrocytomas, the favorable predictive influence of MGMT promoter methylation for those with secondary malignant gliomas has been reported by others.13 Given the finding that external beam radiation was generally used as second-line treatment (at the time of malignant transformation), a favorable predictive impact (beyond the unfavorable prognostic influence) of both IDH1 mutations and MGMT promoter methylation, with positive interactions with effects of radiation therapy, can be assumed. IDH1, for example, is critically involved in cytoplasmatic NADP+ production, and impaired enzymatic activity might make glioma cells more vulnerable to oxidative stress induced by radiotherapy.27, 28 The exact interactions of these biomarkers with the applied treatment strategies, however, still need to be elucidated. It remains a matter of speculation whether the favorable influence of IDH1 on postrecurrence survival indicates an independent predictive role of this biomarker or an epiphenomenon of MGMT promoter methylation. The strong association between IDH1 mutations and a specific hypermethylated profile of MGMT in grade II gliomas and secondary malignant gliomas, as demonstrated in recently published studies, might indicate that genetic and epigenetic alterations are not independent events.29, 30

Whether prognostic effects of IDH1 mutations other than those described here exist for oligotumors remains unclear at this moment. Interestingly, even in a study dealing mainly with oligotumors, a trend toward an impaired PFS in IDH1-mutated tumors was detectable (35.2 vs 44.5 months), which, however, was not noted by the authors.15

In this study, frequency and prognostic value of IDH2 mutations were not addressed. However, as IDH2 mutations are found to be extremely rare events in IDH1-negative astrocytomas,2 we do not expect any bias concerning the prognostic relevance of mutational IDH1 status in our study population.

Among the investigated biomarkers, only a mutated TP53 status gained unfavorable prognostic impact on both PFS and OS (which was in accordance with the findings of our previous work), indicating a pure prognostic role of this biomarker in astrocytomas.18 The unfavorable impact of IDH1 mutations on PFS, however, dominates that of TP53 mutations in multivariate models, leaving the TP53 mutational status only as an independent prognostic factor for length of survival in multivariate models. Loss of heterozygosity on 1p/19q could not be determined in our study; the prognostic relevance of this biomarker still remains to be elucidated for astrocytomas.

How mutations in metabolic pathways contribute to pathogenesis and prognosis is controversial. Recently Dang et al demonstrated that R132 mutations in IDH1 resulted in a gain of function in cells' ability to produce 2-hydroxyglutarate, which is thought to be involved in tumorigenesis and tumor progression8; 100-fold higher levels of 2-hydroxyglutarate have been found in human malignant gliomas harboring IDH1 mutations. However, whereas pathological accumulation of the L-2-hydroxyglutarate enantiomer has been linked to increased risk of gliomas,31 D-2-hydroxyglutarate, which is generated by mutant IDH1, has been shown to be associated with encephalopathy, cardiopathy, and other disease, but not with neoplasias and particularly not with brain tumors.10, 32 Thus, the hypothesis that D-2-hydroxyglutarate is a causative oncometabolite in gliomas needs further investigation. It is noteworthy within this context that prognostic unfavorable effects of IDH1 mutations have also been described for acute myeloid leukemia (AML). Patients with AML experienced shorter event-free survival and higher cumulative risk for relapse in the case of IDH1 mutations.33

IDH1 mutations are thought to precede TP53 mutations or 1p/19q deletions; IDH1-mutated precursor cells might give rise to either astrocytomas or oligotumors after additional acquisition of TP53 mutations or 1p/19q codeletion.2, 34 Our results point in the same direction for the majority of tumors. In 94% of tumors harboring a mutated TP53 status, an additional IDH1 mutation was observed. The subgroup of tumors with wild-type IDH1 (22% of this series) and those rare astrocytomas with a TP53 mutation alone (3.5% of this series), however, indicate that the described model of gliomagenesis suggesting an initiation role of IDH1 is not universally valid. Moreover, considering both the strong correlation between IDH1 mutations and MGMT promoter methylation and their similar impact on outcome in the current report, it remains a matter of speculation which of these 2 molecular events occurs earlier in gliomagenesis.

FUNDING SOURCES

  1. Top of page
  2. Abstract
  3. MATERIALS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. FUNDING SOURCES
  7. REFERENCES

Supported by the German Research Foundation (Deutsche Forschungsgemeinschaft) (PE 758/1-1) and the German Cancer Aid (Deutsche Krebshilfe).

CONFLICT OF INTEREST DISCLOSURES

The authors made no disclosures.

REFERENCES

  1. Top of page
  2. Abstract
  3. MATERIALS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. FUNDING SOURCES
  7. REFERENCES
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