Modern brain tumor imaging

Proton MR Spectroscopy and Diffusion MR Imaging Monitoring to Predict Tumor Response to Interstitial Photodynamic Therapy for Glioblastoma

Despite recent progress in conventional therapeutic approaches, the vast majority of glioblastoma recur locally, indicating that a more aggressive local therapy is required. Interstitial photodynamic therapy (iPDT) appears as a very promising and complementary approach to conventional therapies. However, an optimal fractionation scheme for iPDT remains the indispensable requirement. To achieve that major goal, we suggested following iPDT tumor response by a non-invasive imaging monitoring. Nude rats bearing intracranial glioblastoma U87MG xenografts were treated by iPDT, just after intravenous injection of AGuIX® nanoparticles, encapsulating PDT and imaging agents. Magnetic Resonance Imaging (MRI) and Magnetic Resonance Spectroscopy (MRS) allowed us an original longitudinal follow-up of post-treatment effects to discriminate early predictive markers. We successfully used conventional MRI, T2 star (T2*), Diffusion Weighted Imaging (DWI) and MRS to extract relevant profiles on tissue cytoarchitectural alterations, local vascular disruption and metabolic information on brain tumor biology, achieving earlier assessment of tumor response. From one day post-iPDT, DWI and MRS allowed us to identify promising markers such as the Apparent Diffusion Coefficient (ADC) values, lipids, choline and myoInositol levels that led us to distinguish iPDT responders from non-responders. All these responses give us warning signs well before the tumor escapes and that the growth would be appreciated.

Simultaneous 11C-Methionine Positron Emission Tomography/Magnetic Resonance Imaging of Suspected Primary Brain Tumors

Introduction

The objective of this study was to assess the diagnostic value of integrated 11C- methionine PET/MRI for suspected primary brain tumors, in comparison to MRI alone.

Material and Methods

Forty-eight consecutive patients with suspected primary brain tumor were prospectively enrolled for an integrated 11C-methionine PET/MRI. Two neuro-radiologists separately evaluated the MRI alone and the integrated PET/MRI data sets regarding most likely diagnosis and diagnostic confidence on a 5-point scale. Reference standard was histopathology or follow-up imaging.

Results

Fifty-one suspicious lesions were detected: 16 high-grade glioma and 25 low-grade glioma. Ten non-malignant cerebral lesions were described by the reference standard. MRI alone and integrated PET/MRI each correctly classified 42 of the 51 lesions (82.4%) as neoplastic lesions (WHO grade II, III and IV) or non-malignant lesions (infectious and neoplastic lesions). Diagnostic confidence for all lesions, low-grade astrocytoma and high-grade astrocytoma (3.7 vs. 4.2, 3,1 vs. 3.8, 4.0 vs. 4,7) were significantly (p < 0.05) better with integrated PET/MRI than in MRI alone.

Conclusions

The present study demonstrates the high potential of integrated 11C-methionine-PET/MRI for the assessment of suspected primary brain tumors. Although integrated methionine PET/MRI does not lead to an improvement of correct diagnoses, diagnostic confidence is significantly improved.

White Matter Change Revealed by Diffusion Tensor Imaging in Gliomas

Background

Tumor-related white matter change is detected at late stages with magnetic resonance imaging (MRI), when mass effect or prominent edema is present. We analyzed if diffusion tensor imaging (DTI) white matter change earlier than conventional MRI.

Methods

Twenty-six patients with gliomas (World Health Organization grade II, 5; grade III, 12; and grade IV, 9) within 2 cm from the posterior limb of the internal capsule (IC) were studied. Fifteen normal adults were enrolled as controls. Fluid attenuation inversion recovery MRI showed a high signal change at the posterior limb of the IC (HSIC) in 9 patients with grade III or IV gliomas. We classified the gliomas as WHO grade II (gliomas II), grade III or IV without HSIC [gliomas III/IV(-)] and grade III or IV with HSIC [gliomas III/IV(+)], as an indicator of the increase in the severity of the white matter changes. Fractional anisotropy (FA) and apparent diffusion coefficients (ADC) were calculated for the pyramidal tract. Tumor progression along pyramidal tract was evaluated by follow-up MRI in 16 patients at 40±18 months.

Results

FA showed no significant difference between gliomas II and control (p=0.694), but was lower in gliomas III/IV(-) and gliomas III/IV(+) (p<0.001). ADCs were higher in gliomas II, gliomas III/IV(-) and gliomas III/IV(+) than control (p<0.001). Tumor progression was detected in 2/16 patients.

Conclusion

DTI detected white matter changes that appeared to be normal in MRI. ADC changed even in low grade glioma, indicating ADC may be a better parameter for the early detection of white matter change.

Diffusion weighted imaging: Technique and applications

Diffusion weighted imaging (DWI) is a method of signal contrast generation based on the differences in Brownian motion. DWI is a method to evaluate the molecular function and micro-architecture of the human body. DWI signal contrast can be quantified by apparent diffusion coefficient maps and it acts as a tool for treatment response evaluation and assessment of disease progression. Ability to detect and quantify the anisotropy of diffusion leads to a new paradigm called diffusion tensor imaging (DTI). DTI is a tool for assessment of the organs with highly organised fibre structure. DWI forms an integral part of modern state-of-art magnetic resonance imaging and is indispensable in neuroimaging and oncology. DWI is a field that has been undergoing rapid technical evolution and its applications are increasing every day. This review article provides insights in to the evolution of DWI as a new imaging paradigm and provides a summary of current role of DWI in various disease processes.

Radiogenomics of Glioblastoma: Machine Learning-based Classification of Molecular Characteristics by Using Multiparametric and Multiregional MR Imaging Features

Purpose To evaluate the association of multiparametric and multiregional magnetic resonance (MR) imaging features with key molecular characteristics in patients with newly diagnosed glioblastoma. Materials and Methods Retrospective data evaluation was approved by the local ethics committee, and the requirement to obtain informed consent was waived. Preoperative MR imaging features were correlated with key molecular characteristics within a single-institution cohort of 152 patients with newly diagnosed glioblastoma. Preoperative MR imaging features (n = 31) included multiparametric (anatomic and diffusion-, perfusion-, and susceptibility-weighted images) and multiregional (contrast-enhancing regions and hyperintense regions at nonenhanced fluid-attenuated inversion recovery imaging) information with histogram quantification of tumor volumes, volume ratios, apparent diffusion coefficients, cerebral blood flow, cerebral blood volume, and intratumoral susceptibility signals. Molecular characteristics determined included global DNA methylation subgroups (eg, mesenchymal, RTK I "PGFRA," RTK II "classic"), MGMT promoter methylation status, and hallmark copy number variations (EGFR, PDGFRA, MDM4, and CDK4 amplification; PTEN, CDKN2A, NF1, and RB1 loss). Univariate analyses (voxel-lesion symptom mapping for tumor location, Wilcoxon test for all other MR imaging features) and machine learning models were applied to study the strength of association and discriminative value of MR imaging features for predicting underlying molecular characteristics. Results There was no tumor location predilection for any of the assessed molecular parameters (permutation-adjusted P > .05). Univariate imaging parameter associations were noted for EGFR amplification and CDKN2A loss, with both demonstrating increased Gaussian-normalized relative cerebral blood volume and Gaussian-normalized relative cerebral blood flow values (area under the receiver operating characteristics curve: 63%-69%, false discovery rate-adjusted P < .05). Subjecting all MR imaging features to machine learning-based classification enabled prediction of EGFR amplification status and the RTK II glioblastoma subgroup with a moderate, yet significantly greater, accuracy (63% for EGFR [P < .01], 61% for RTK II [P = .01]) than prediction by chance; prediction accuracy for all other molecular parameters was not significant. Conclusion The authors found associations between established MR imaging features and molecular characteristics, although not of sufficient strength to enable generation of machine learning classification models for reliable and clinically meaningful prediction of molecular characteristics in patients with glioblastoma. ^© RSNA, 2016 Online supplemental material is available for this article.

MR perfusion-weighted imaging in the evaluation of high-grade gliomas after treatment: a systematic review and meta-analysis

BACKGROUND

Distinction between tumor and treatment related changes is crucial for clinical management of patients with high-grade gliomas. Our purpose was to evaluate whether dynamic susceptibility contrast-enhanced (DSC) and dynamic contrast enhanced (DCE) perfusion-weighted imaging (PWI) metrics can effectively differentiate between recurrent tumor and posttreatment changes within the enhancing signal abnormality on conventional MRI.

METHODS

A comprehensive literature search was performed for studies evaluating PWI-based differentiation of recurrent tumor and posttreatment changes in patients with high-grade gliomas (World Health Organization grades III and IV). Only studies published in the "temozolomide era" beginning in 2005 were included. Summary estimates of diagnostic accuracy were obtained by using a random-effects model.

RESULTS

Of 1581 abstracts screened, 28 articles were included. The pooled sensitivities and specificities of each study's best performing parameter were 90% and 88% (95% CI: 0.85-0.94; 0.83-0.92) and 89% and 85% (95% CI: 0.78-0.96; 0.77-0.91) for DSC and DCE, respectively. The pooled sensitivities and specificities for detecting tumor recurrence using the 2 most commonly evaluated parameters, mean relative cerebral blood volume (rCBV) (threshold range, 0.9-2.15) and maximum rCBV (threshold range, 1.49-3.1), were 88% and 88% (95% CI: 0.81-0.94; 0.78-0.95) and 93% and 76% (95% CI: 0.86-0.98; 0.66-0.85), respectively.

CONCLUSIONS

PWI-derived thresholds separating viable tumor from treatment changes demonstrate relatively good accuracy in individual studies. However, because of significant variability in optimal reported thresholds and other limitations in the existing body of literature, further investigation and standardization is needed before implementing any particular quantitative PWI strategy across institutions.

A restricted signature of serum miRNAs distinguishes glioblastoma from lower grade gliomas

Background

Malignant gliomas are the most common primary brain tumors in adults and challenging cancers for diagnosis and treatment. They remain a disease for which non-invasive, diagnostic and/or prognostic novel biomarkers are highly desirable. Altered microRNA (miRNA) profiles have been observed in tumor tissues and biological fluids. To date only a small set of circulating/serum miRNA is found to be differentially expressed in brain tumors compared to normal controls.

Here a restricted signature of circulating/serum miRNA including miR-15b*,-23a, −99a, −125b, −133a, −150*, −197, −340, −497, −548b-5p and let-7c were investigated as potential non-invasive biomarkers in the diagnosis of glioma patients.

Methods

Serum and tissues miRNAs expression in patients with brain cancers (n = 30) and healthy controls (n = 15) were detected by quantitative real-time polymerase chain reaction (qRT-PCR). Relative expression was calculated using the comparative Ct method. Statistical significance (p ≤ 0,05) was determined using the Mann–Whitney rank sum and Fisher’s exact test. Diagnostic accuracy of miRNAs in distinguishing glioblastoma multiforme (GBM) from lower grade cancer was assessed by the Receiver Operating Characteristic (ROC) curve analysis.

To validate the role of the identified miRNAs in cancer a comprehensive literature search was conducted using PubMed, Web of Science (Core Collection) and Scopus databases.

Results

We observed a decrease of miR-497 and miR-125b serum levels depending on tumor stages with reduced level in GBM than lower grade tumors. The ROC curve analysis distinguishing GBM from lower grade cases yielded an area under the curve (AUC) of 0.87 (95 % confidence interval (CI) = 0.712–1) and of 0.75 (95 % CI = 0.533–0.967) for miR-497 and -125b, respectively. GBM patients are more likely to show a miR-497 and -125b down-regulation than the lower grade group (p = 0.002 and p = 0.024, respectively). These results were subsequently compared with evidence from 19 studies included in the final systematic review.

Conclusions

Although multiple biomarkers are currently leveraged in the clinic to detect specific cancer types, no such standard blood biomolecules are used as yet in gliomas. Our data suggest that serum miR-497 and -125b could be a novel diagnostic markers with good perspectives for future clinical applications in patients with glioma.

Targeting MT1-MMP as an ImmunoPET-Based Strategy for Imaging Gliomas

BACKGROUND

A critical challenge in the management of Glioblastoma Multiforme (GBM) tumors is the accurate diagnosis and assessment of tumor progression in a noninvasive manner. We have identified Membrane-type 1 matrix metalloproteinase (MT1-MMP) as an attractive biomarker for GBM imaging since this protein is actively involved in tumor growth and progression, correlates with tumor grade and is closely associated with poor prognosis in GBM patients. Here, we report the development of an immunoPET tracer for effective detection of MT1-MMP in GBM models.

METHODS

An anti-human MT1-MMP monoclonal antibody (mAb), LEM2/15, was conjugated to p-isothiocyanatobenzyl-desferrioxamine (DFO-NCS) for 89Zr labeling. Biodistribution and PET imaging studies were performed in xenograft mice bearing human GBM cells (U251) expressing MT1-MMP and non-expressing breast carcinoma cells (MCF-7) as negative control. Two orthotopic brain GBM models, patient-derived neurospheres (TS543) and U251 cells, with different degrees of blood-brain barrier (BBB) disruption were also used for PET imaging experiments.

RESULTS

89Zr labeling of DFO-LEM2/15 was achieved with high yield (>90%) and specific activity (78.5 MBq/mg). Biodistribution experiments indicated that 89Zr-DFO-LEM2/15 showed excellent potential as a radiotracer for detection of MT1-MMP positive GBM tumors. PET imaging also indicated a specific and prominent 89Zr-DFO-LEM2/15 uptake in MT1-MMP+ U251 GBM tumors compared to MT1-MMP- MCF-7 breast tumors. Results obtained in orthotopic brain GBM models revealed a high dependence of a disrupted BBB for tracer penetrance into tumors. 89Zr-DFO-LEM2/15 showed much higher accumulation in TS543 tumors with a highly disrupted BBB than in U251 orthotopic model in which the BBB permeability was only partially increased. Histological analysis confirmed the specificity of the immunoconjugate in all GBM models.

CONCLUSION

A new anti MT1-MMP-mAb tracer, 89Zr-DFO-LEM2/15, was synthesized efficiently. In vivo validation showed high-specific-contrast imaging of MT1-MMP positive GBM tumors and provided strong evidence for utility of MT1-MMP-targeted immunoPET as an alternate to nonspecific imaging of GBM.

Targeting cancer stem-like cells in glioblastoma and colorectal cancer through metabolic pathways

Cancer stem-like cells (CSCs) are thought to be the main cause of tumor occurrence, progression and therapeutic resistance. Strong research efforts in the last decade have led to the development of several tailored approaches to target CSCs with some very promising clinical trials underway; however, until now no anti-CSC therapy has been approved for clinical use. Given the recent improvement in our understanding of how onco-proteins can manipulate cellular metabolic networks to promote tumorigenesis, cancer metabolism research may well lead to innovative strategies to identify novel regulators and downstream mediators of CSC maintenance. Interfering with distinct stages of CSC-associated metabolics may elucidate novel, more efficient strategies to target this highly malignant cell population. Here recent discoveries regarding the metabolic properties attributed to CSCs in glioblastoma (GBM) and malignant colorectal cancer (CRC) were summarized. The association between stem cell markers, the response to hypoxia and other environmental stresses including therapeutic insults as well as developmentally conserved signaling pathways with alterations in cellular bioenergetic networks were also discussed. The recent developments in metabolic imaging to identify CSCs were also summarized. This summary should comprehensively update basic and clinical scientists on the metabolic traits of CSCs in GBM and malignant CRC.

Perfusion magnetic resonance imaging provides additional information as compared to anatomical imaging for decision-making in vestibular schwannoma

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DSC/ASL-MRI can be acquired in growing VS with sufficient image quality.

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In most patients DSC and ASL techniques provide similar qualitative scores.

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These techniques can be of importance in future decision-making.

Objective

The added value of perfusion MRI for decision-making in vestibular schwannoma (VS) patients is unknown. MRI offers two perfusion methods: the first employing contrast agent (dynamic susceptibility contrast (DSC)-MRI) that provides information on cerebral blood volume (CBV) and cerebral blood flow (CBF), the second by magnetic labeling of blood (arterial spin labeling (ASL)-MRI), providing CBF-images. The goal of the current study is to investigate whether DSC and ASL perfusion MRI provides complimentary information to current anatomical imaging in treatment selection process of VS.

Methods

Nine patients with growing VS with extrameatal diameter >9 mm were included (>2 mm/year and 20% volume expansion/year) and one patient with 23 mm extrameatal VS without growth. DSC and ASL perfusion MRI were obtained on 3 T MRI. Perfusion in VS was scored as hyperintense, hypointense or isointense compared to the contralateral region.

Results

Seven patients showed hyperintense signal on DSC and ASL sequences. Three patients showed iso- or hypointense signal on at least one perfusion map (1 patient hypointense on both DSC-MRI and ASL; 1 patient isointense on DSC-CBF; 1 patient isointense on ASL). All patients showed enhancement on post-contrast T1 anatomical scan.

Conclusion

Perfusion MR provides additional information compared to anatomical imaging for decision-making in VS.

Imaging of Brain Tumors with Copper-64 Chloride: Early Experience and Results

OBJECTIVES

To conduct the first investigational study that is aimed at evaluating the ability of the simple salt (64)CuCl2 to diagnose cerebral tumors in patients affected by glioblastoma multiforme (GBM).

METHODS

Nineteen patients with a documented history and radiologic evidence of brain tumors were enrolled in the study. Eighteen patients were diagnosed with GBM, and one patient was diagnosed with grade II astrocytoma. After initial cerebral magnetic resonance imaging (MRI), patients were administered with (64)CuCl2 (13 MBq/kg) and brain positron emission tomography (PET)/computed tomography (CT) imaging was performed at 1, 3, and 24 hours after administration. Standardized uptake values (SUVs) were calculated and used to figure out the pharmacokinetic profile of the tracer. Absorbed radiation doses were estimated using OLINDA/EXM.

RESULTS

Copper-64 chloride clearly visualized brain cancerous lesions within 1 hour after injection, with stable retention of radioactivity at 3 and 24 hours. Excellent agreement was found between PET/CT and MRI. No uptake of the tracer was observed in low-grade astrocytoma. The agent cleared rapidly from the blood and was mostly excreted through the liver, without significant kidney washout. Analysis of time variation of SUVmax values showed persistent uptake in malignant tissues with a slight increase of radioactive concentration at 24 hours.

CONCLUSIONS

Copper-64 chloride has favorable biological properties for brain imaging and warrants further investigation as a diagnostic tracer for GBM.

Time lapse in vivo microscopy reveals distinct dynamics of microglia-tumor environment interactions-a new role for the tumor perivascular space as highway for trafficking microglia

Microglial cells are critical for glioma growth and progression. However, only little is known about intratumoral microglial behavior and the dynamic interaction with the tumor. Currently the scarce understanding of microglial appearance in malignant gliomas merely originates from histological studies and in vitro investigations. In order to understand the pattern of microglia activity, motility and migration we designed an intravital study in an orthotopic murine glioma model using CX3CR1-eGFP(GFP/wt) mice. We analysed the dynamics of intratumoral microglia accumulation and activity, as well as microglia/tumor blood vessel interaction by epi-illumination and 2-photon laser scanning microscopy. We further investigated cellular and tissue function, including the enzyme activity of intratumoral and microglial NADPH oxidase measured by in vivo fluorescence lifetime imaging. We identified three morphological phenotypes of tumor-associated microglia cells with entirely different motility patterns. We found that NADPH oxidase activation is highly divergent in these microglia subtypes leading to different production levels of reactive oxygen species (ROS). We observed that microglia motility is highest within the perivascular niche, suggesting relevance of microglia/tumor blood vessel interactions. In line, reduction of tumor blood vessels by antivascular therapy confirmed the relevance of the tumor vessel compartment on microglia biology in brain tumors. In summary, we provide new insights into in vivo microglial behavior, regarding both morphology and function, in malignant gliomas. GLIA 2016;64:1210-1226.

Diagnosis and New Treatment Modalities for Glioblastoma: Do They Improve Patient Survival?

Central nervous system (CNS) malignances include tumors of the brain and spinal cord. Taking into account the cell type where they originate from, there are almost 120 different types of CNS tumors. Benign tumors are not aggressive and normally do not invade other organs; however, they require surgical removal before they alter the surrounding brain functions. Primary malignant brain tumors commonly include astrocytomas, oligodendrogliomas, and ependimomas, where astrocytomas represent around 76%. The World Health Organization (WHO) has defined four histological grades of astrocytomas that range from the less aggressive tumors (grade I) to highly malignant tumors (grade IV). These grade IV tumors, also called glioblastoma (GBM), are the most aggressive of the primary malignant brain tumors. Patients with GBM have a median survival of 12 to 15 months. Current treatment for GBM includes surgery, radiotherapy and chemotherapy. Although there have been some advances in diagnosis and treatment, there is still no optimal treatment available for GBMs. In this review, we will discuss the approaches for GBM diagnosis and treatment, with a special emphasis to post-treatment imaging, and whether novel targeted therapies have impacted the survival of GBM patients. In addition, we will discuss clinical trials and the future of GBM diagnosis and treatment.

Pediatric thalamic tumors in the MRI era: a Canadian perspective

BACKGROUND

Thalamic gliomas are rare. The natural history is unpredictable, and the optimal management of these tumors in children is poorly defined. The aim was to identify outcomes, prognostic factors, and response to various modalities of treatment in a relatively large population of pediatric thalamic tumors from many centers within a fairly homogeneous health care system.

METHODS

We performed a Canadian multicenter retrospective review of pediatric thalamic tumors presenting during the MRI era (1989-2012). Radiology and pathology were reviewed by central independent reviewers. Paraffin shavings for RNA extraction were taken and tested for fusion events involving KIAA1549:BRAF. Tumors were classified as unilateral or bithalamic based on their origin on imaging. Univariate and multivariate analyses on factors influencing survival were performed.

RESULTS

Seventy-two thalamic tumors were identified from 11 institutions. Females represented 53% of the study population, and the mean age at presentation was 8.9 years. Sixty-two tumors were unilateral and 10 bithalamic. Unilateral tumors had a greater propensity to grow inferiorly towards the brainstem. These tumors were predominantly low grade in comparison to bithalamic tumors which were high-grade astrocytomas. The 5-year overall survival was 61 ± 13% for unithalamic tumors compared to 37 ± 32% for bithalamic tumors (p = 0.097). Multivariate analysis indicated tumor grade as the only significant prognostic factor for unithalamic tumors. Six unilateral tumors, all low grade, were BRAF fusion positive.

CONCLUSION

Unilateral and bilateral thalamic tumors behave differently. Surgical resection is an appropriate treatment option in unilateral tumors, most of which are low grade, but outcome is not related to extent of resection (EOR). Bilateral thalamic tumors have a poorer prognosis, but the occasional patient does remarkably well. The efficacy of chemotherapy and radiotherapy has not been clearly demonstrated. Novel therapeutic approaches are required to improve the prognosis for malignant unilateral thalamic tumors and bilateral thalamic tumors.

Integration of 2-hydroxyglutarate-proton magnetic resonance spectroscopy into clinical practice for disease monitoring in isocitrate dehydrogenase-mutant glioma

BACKGROUND

The majority of WHO grades II and III gliomas harbor a missense mutation in the metabolic gene isocitrate dehydrogenase (IDH) and accumulate the metabolite R-2-hydroxyglutarate (R-2HG). Prior studies showed that this metabolite can be detected in vivo using proton magnetic-resonance spectroscopy (MRS), but the sensitivity of this methodology and its clinical implications are unknown.

METHODS

We developed an MR imaging protocol to integrate 2HG-MRS into routine clinical glioma imaging and examined its performance in 89 consecutive glioma patients.

RESULTS

Detection of 2-hydroxyglutarate (2HG) in IDH-mutant gliomas was closely linked to tumor volume, with sensitivity ranging from 8% for small tumors (<3.4 mL) to 91% for larger tumors (>8 mL). In patients undergoing 2HG-MRS prior to surgery, tumor levels of 2HG corresponded with tumor cellularity but not with tumor grade or mitotic index. Cytoreductive therapy resulted in a gradual decrease in 2HG levels with kinetics that closely mirrored changes in tumor volume.

CONCLUSIONS

Our study demonstrates that 2HG-MRS can be linked with routine MR imaging to provide quantitative measurements of 2HG in glioma and may be useful as an imaging biomarker to monitor the abundance of IDH-mutant tumor cells noninvasively during glioma therapy and disease monitoring.

Large-volume low apparent diffusion coefficient lesions predict poor survival in bevacizumab-treated glioblastoma patients

BACKGROUND

Glioblastomas treated with bevacizumab may develop low-signal apparent diffusion coefficient (low-ADC) lesions, which may reflect increased tumor cellularity or atypical necrosis. The purpose of this study was to examine the relationship between low-ADC lesions and overall survival (OS). We hypothesized that growing low-ADC lesions would be associated with shorter OS.

METHODS

We retrospectively identified 52 patients treated with bevacizumab for the first (n = 42, 81%) or later recurrence of primary glioblastoma, who had low-ADC lesions and 2 post-bevacizumab scans ≤90 days apart. Low-ADC lesion volumes were measured, and normalized 5th percentile histogram low-ADC values were recorded. Using OS as the primary endpoint, semiparametric Cox models were fitted to ascertain univariate and multivariate hazard ratios (HRs) with significance at P = .05.

RESULTS

Median OS was 9.1 months (95% CI = 7.2-14.3). At the second post-bevacizumab scan, the volume of the low-ADC lesion (median: 12.94 cm(3)) was inversely associated with OS, with larger volumes predicting shorter OS (HR = 1.014 [95% CI = 1.003-1.025], P = .009). The percent change in low-ADC volume (median: 6.8%) trended toward increased risk of death with growing volumes (P = .08). Normalized 5th percentile low-ADC value and its percent change were not associated with OS (P > .51). Also correlated with shorter OS were the pre-bevacizumab nonenhancing volume (P = .025), the first post-bevacizumab enhancing volume (P = .040), and the second post-bevacizumab enhancing volume (P = .004).

CONCLUSIONS

The volume of low-ADC lesions at the second post-bevacizumab scan predicted shorter OS. This suggests that low-ADC lesions may be considered important imaging markers and included in treatment decision algorithms.