Ha Son Nguyen1, Nelson Milbach2, Sarah L Hurrell2, Elizabeth Cochran3, Jennifer Connelly4, Mona Al-Gizawiy2, Joseph Bovi5, Scott D Rand2, Kathleen M Schmainda2, and Peter S. LaViolette2,6
1Neurosurgery, Medical College of Wisconsin, Milwaukee, WI, United States, 2Radiology, Medical College of Wisconsin, Milwaukee, WI, United States, 3Pathology, Medical College of Wisconsin, Milwaukee, WI, United States, 4Neurology, Medical College of Wisconsin, Milwaukee, WI, United States, 5Radiation Oncology, Medical College of Wisconsin, Milwaukee, WI, United States, 6Biophysics, Milwaukee, WI, United States
Synopsis
It is the standard of
care to initiate bevacizumab therapy for patients with recurrent glioblastoma. Some patients
develop areas of diffusion restriction on diffusion imaging following the onset of therapy. We recruited five patients with this
condition to donate their brains postmortem.
A histological analysis was performed and compared to MR images to
discover what caused the diffusion restriction.
It was found to be coagulative necrosis surrounded by viable
hypercellular tumor. A second population study shows that patients with progressively expanding diffusion restriction had a significantly lower
survival compared to those without.Intended Audience
Clinicians
and scientists interested in brain tumor patients and bevacizumab
treatment
Purpose
The current
standard of care for recurrent glioblastoma (GBM) involves treatment with the
anti-vascular endothelial growth factor (VEGF) drug bevacizumab. Curiously, a
subset of patients develops focal regions of diffusion restriction following
the onset of therapy. Conflicting studies have shown these regions to be either
diffusion restricted necrosis (DRN)
1 or exclusively
hypercellular tumor
2. One recent manuscript reports
regions of both, where the DRN was shown to have significantly lower apparent
diffusion coefficient (ADC) values
3. This study
explores regions of bevacizumab induced diffusion restriction in human whole
brain samples and determines appropriate ADC cutoffs for differentiating DRN
from viable hypercellular tumor. An additional population analysis shows overall survival consequences
dependent on whether these lesions appear and whether they progress.
Methods
Part 1:
(histological validation):
Patient Population Five patients with recurrent GBM and regions of focal
diffusion restriction (while on bevacizumab therapy) were recruited for brain
donation and enrolled into this study.
Imaging Prior to death patients
were clinically imaged using diffusion weighted imaging (DWI), T1 pre and post
gadolinium, and T2 weighted images. Apparent diffusion coefficient (ADC) maps
were calculated from DWI.
Histology
Processing Post-mortem pathological slicing of the brains was done
using customized slicing jigs 3d-printed for each patient. Areas of diffusion
restriction were defined using radiological criteria and histological samples
were taken from regions co-localized with diffusion restriction. Samples were paraffin embedded,
H&E stained, and digitized for interpretation. Each sample was graded to
differentiate necrotic regions from viable tumor. Pathologist-confirmed coagulative
necrosis and hypercellularity were then compared to MR imaging. Figure 1 shows
one patient’s scans compared to matching brain slice with targeted section
sampled and stained. Figure 1 also shows a comparison of regions within the
diffusion restriction zone and directly neighboring regions. ADC values from
regions of diffusion restricted necrosis were compared to those classified as
hypercellular. An ROC analysis was performed iteratively adjusting ADC cut-off
values until a maximal area under the curve (AUC) was obtained for each
patient.
Part 2 (population study):
Patient Population 64 patients
undergoing bevacizumab treatment for recurrent GBM were retrospectively
analyzed to determine if diffusion restricted lesions developed following
treatment onset. Patients were separated into three groups, no diffusion
restriction developed (NDR), diffusion restriction that progressively grew
within 3months (PrDR), and patients that developed diffusion restriction that
was stable for at least 3 months (StDR). The overall survival (OS) was then
compared using Kaplan-Meier curves and a log-rank test.
Results
Part 1: Regions of diffusion-restricted
necrosis had significantly lower ADC values than nearby hypercellularity. The average ADC threshold (shown in table 1) that
best differentiated these tissue types was 0.6996x10-3mm2/s corresponding
to an average AUC of 0.7364. In four of the five patients, the diffusion-restricted necrosis was
progressively growing at the time of the patient’s final scan. The necrotic
regions were surrounded by viable hypercellular non-enhancing tumor. The
patient without progressively growing diffusion restriction had recurrent tumor
elsewhere, not directly adjacent to the diffusion restriction.
Part 2: Figure 3 shows the survival curves
comparing NDR, PrDR and StDR, where StDR patients had a significantly greater
OS than the NDR group, while the PrDR group significantly lower OS than the NDR
group (p<0.05). It should be noted that at the time of
death, all diffusion-restricted lesions were expanding for both the StDR and
PrDR groups.
Discussion
We
pathologically confirmed that progressively expanding diffusion restriction in
patients undergoing bevacizumab treatment indicated coagulative necrosis
surrounded by viable hypercellular tumor. We also determined an optimal ADC
cutoff for differentiating diffusion-restricted necrosis from hypercellular
tumor. Population-wise, patients with progressively growing regions of
diffusion restriction have decreased overall survival suggesting the lesions
themselves are necrosis surrounded by viable tumor when expanding. Patients
with stable lesions however showed increased OS over the NDR group. Further
research is necessary to establish the biological basis for bevacizumab causing
these lesions.
Acknowledgements
Advancing a Healthier Wisconsin
MCW Research Affairs Committee
NCI U01-CA176110-01A1
References
1. Farid N, Almeida-Freitas DB, White NS,
et al. Combining diffusion and perfusion differentiates tumor from bevacizumab-related
imaging abnormality (bria). J Neurooncol.
2014;120(3):539-546.
2. Gupta
A, Young RJ, Karimi S, et al. Isolated diffusion restriction precedes the
development of enhancing tumor in a subset of patients with glioblastoma. AJNR Am J Neuroradiol. 2011;32(7):1301-1306.
3. LaViolette
PS, Mickevicius NJ, Cochran EJ, et al. Precise ex vivo histological validation
of heightened cellularity and diffusion-restricted necrosis in regions of dark
apparent diffusion coefficient in 7 cases of high-grade glioma. Neuro Oncol. 2014;16(12):1599-1606.