Keywords
glioma - Protein Kinase - KDR
Introduction
Gliomas are the most frequent neoplasms of the central nervous system (CNS) originating
from glial cells in older adults (mean age of 65 years). They are diffusely infiltrative
tumors that affect the surrounding brain tissue. Glioblastoma multiforme is the most
malignant type of glioma, while pilocytic astrocytoma is the least. Based on the histopathological
analysis, gliomas are graded into four types (I–IV). The first type, Grade I glioma,
is easily curable as it is usually benign. The second type, Grade II glioma, also
called lower grade glioma (LGG), is often encountered in young adults. LGG is characterized
by seizures and lesions in the temporal, frontal, or insular lobes. Most glioma cases
detected belong to Grade III or Grade IV. In the United States, there are six cases
of gliomas diagnosed per 100,000 people every year.[1] In India, 1 to 4 brain tumors per 100,000 cases occur. Glioblastoma multiforme (GBM)
accounts for 18% of all primary brain tumors and 45.9% of all glioma tumors (data
from Population-based Cancer Registry, GCRI). Thus, overall, the epidemiological data
on GBM tumors indicates that the incidence of this malignancy is increasing in India.[2] Genetic factors, along with environmental influence, are known to cause gliomas.
LGG in a young adult may be more genetic in etiology. As more genetic studies are
being done, several new genetic biomarkers are found to be associated with specific
cancers. We report a case of recurrent gliomas, with increasing severity, in a young
individual found to have a germline mutation in the KDR gene.
Case Report
A 35-year-old man with recurrent glioma was diagnosed with LGG in 2013, for which
he underwent right-sided craniotomy and radiation therapy. This time he came in with
aggressive secondary GBM, likely originating from the previous LGG. The patient presented
with symptoms of generalized seizures and ECOG (Eastern Cooperative Oncology Group)
performance status of level 3. Magnetic resonance imaging (MRI) brain showed right
frontal craniotomy changes, including meningocele, along with new lesions in the right
frontal lobe. The patient underwent a repeat right craniotomy and ventriculoperitoneal
shunt placement. Biopsy of the lesion showed areas of necrosis with microvascular
proliferation and multinucleated tumor cells. The patient was diagnosed as IDH mutated, ATRX mutated, GBM WHO grade IV. The patient was started on antiepileptics. He was also
started on the chemotherapy agent Lomustine.
The attending physician sought tumor profiling and multigene panel testing to aid
in drug decision-making of Foods and Drug Administration (FDA)-approved therapeutic
molecules for approved biomarkers because the genetic factor was assumed to be linked
to carcinogenesis. They investigated the correlation between non-routinely assessed
oncogenes from a panel of 351 genes (Agilent Cancer Core Panel; [Supplementary Table S1], available online only>) and clinical, morphological, and molecular features to
isolate gene variants, which might hold a diagnostic or prognostic significance and
potential relevance for treatment. The DNA was extracted from FFPE blocks using the
MN NucleoSpin DNA FFPE XS kit, followed by NGS Library preparation using SureSelect
XT HS2 DNA system, a hybrid capture-based technology that includes 351 genes and subjected
to paired-end sequencing on Illumina Novoseq 6000 platform. A total of 9.5 GB of raw
data were generated, followed by the quality screening of raw FASTQ files, adapter
trimming, mapping of raw data to the hg38 reference genome and generation of Sam/Bam
files. VCF file was generated using the GATK 4.2.2 pipeline. Annotation of VCF file
was using Ensembl VEP and Oncotator.
Results of Gene Panel test: Variant analysis in the targeted genes found a homozygous missense variant in exon
25 of the KDR gene (chr4:55089425C > T; NM_002253.4) ([Fig. 1]). The single nucleotide substitution of C > T results in an amino acid substitution
of glutamine for arginine at codon 1118 (c.3353G > A; p.Arg1118Gln) ([Fig. 2]). The observed KDR gene variant lies in the protein tyrosine and serine/threonine kinase domain of the
KDR protein. Though there are no proven clinical studies yet, and in silico analysis of the KDR gene variant p. Arg1118Gln was found to be probably damaging by PolyPhen-2 (HumVar
and HumDiv) and deleterious by SIFT.
Fig. 1 KDR Gene Variant in IGV.
Fig. 2 Location of KDR Gene Variant (p.Arg1118Gln) (1).
Discussion
The KDR gene encodes a kinase insert domain receptor, also known as VEGFR2,[3] which is a type III receptor tyrosine kinase of the VEGF gene involved in angiogenesis.[4] Angiogenesis plays an essential role in the transition from early stages of cancer
to metastasis or stage IV. Strategies or medications that block VEGF-KDR signaling
successfully inhibit experimental tumor growth, as this is the foremost signaling
step required for the proliferating tumor endothelium.[5] It is well known that many FDA-approved drugs targeting the KDR gene (including apatinib, cabozantinib, pazopanib, and sorafenib) have been applied
to treat renal, gastric, colorectal, and other cancers.[6]
[7]
[8]
[9] A clinical trial in a Chinese cohort is going on to treat recurrent glioblastoma
with apatinib.[10]
Association of KDR gene Mutations in Glioma
Association of KDR gene Mutations in Glioma
Mutations in the KDR gene have been reported in different cancer types, predominantly in melanoma and
non-melanomatic skin cancers ([Supplementary Fig. S1], available online only). The p.Arg1118Gln variant in heterozygous conditions has
previously been reported in glioblastoma, rectal adenocarcinoma, uterine endometrioid
cancer, and colon adenocarcinoma (Resource: cBioportal).[11]
[12] Two different mutations affecting the codon 1118 (p.Arg1118Ter and p.Arg1118Leu)
have previously been reported in patients with glioblastoma multiforme, sarcoma, uterine
endometrioid carcinoma, lung, and colon adenocarcinoma (The AACR Project GENIE Consortium,
2017).[13] KDR p.Arg1118Ter variant is present in 0.02% of AACR GENIE cases and comprised colon
adenocarcinoma, endometrial endometrioid adenocarcinoma, lung adenocarcinoma, and
sarcoma and astrocytoma.[14]
[15]
[16]
The limitation of this case report is that the targeted therapy associated with the
KDR gene in gliomas is under clinical trials only. Though the detected variant was with
a very high variant allele fraction, Sanger validation in paired tumor-normal specimens
may strengthen the authenticity of zygosity. Hence, the present information helps
facilitate further exploration of functional analyses of KDR mutations in gliomas.
Conclusion
This is the first report of the KDR gene variant in a homozygous state reported in a patient diagnosed with glioma. Screening
mutations in protein tyrosine and serine/threonine kinase domain of the KDR will provide
critical insights into the development and progression of glioma in the pediatric
and adult populations. Screening for germline mutations in pediatric cases, it is
strongly recommended to conduct additional testing with paired tumour-normal specimens.
Because GBM, the most aggressive type of glioma, is a vascular tumor, the KDR gene associated with VEGF is probably implicated in tumor growth. Therefore, in young
GBM patients with germline KDR mutations, it might be prudent to give a trial of anti-vascular drugs along with
the conventional treatment regimen.
