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option in malignant gliomas (43). In a Phase II study (ReACT)
(44), bevacizumab-naïve patients in their first or second
relapse with EGFRvIII-expressing GBM were randomized
in to bevacizumab plus either rindopepimut or KLH. As per
the last update 25% of patients treated with rindopepimut
plus bevacizumab remained alive at 2-years compared with
none in the control arm. The median overall survival (OS) with
rindopepimut was 11.3 versus 9.3 months in the control
arm [hazard ratio (HR), 0.53; 95% confidence interval (CI),
0.32–0.88; P=0.0137]. Full response, PFS, and OS data are
awaited. However in the recently reported results using the
same peptide vaccine when added to standard of care as first
line therapy in patients with tumors expressing EGFRvIII in
a Phase III trial, it failed to reach its OS endpoint (45). The
future of using this immunotherapeutic option perhaps lies
more in the recurrent setting when added to antiangiogenic
therapy as indicated by some preclinical data (46).
ATRX MUTATION
The alpha thalassemia/mental retardation syndrome X linked
(ATRX) gene mutations in glioma is primarily seen in in adoles-
cents and young adults. Mutations in ATRX result in loss of
ATRX protein by immunostaining and are thought to mediate
loss of function. These inactivating mutations are known to
correlate with the alternating lengthening of telomeres (ALT)
phenotype and are associated with telomere dysfunction and
other mutations including
IDH1
and TP53, but are mutually
exclusive from 1p/19q-codeletion (47,48). In a large study ALT
phenotype was associated with loss of ATRX protein expression
in both pediatric and adult astrocytomas, suggesting ATRX loss
to be a highly specific biomarker of astrocytic lineage (49). This
has now been incorporated in the decision making algorithm
for differentiating oligodendroglial versus astrocytic origin
of gliomas in the 2016 WHO classification. Given the ease of
detection of this mutation by using immunohistochemistry, it
makes it more accessible and feasible in daily practice. Within
the subgroup of
IDH
-mutant astrocytic tumors, ATRX loss indi-
cates a better prognosis as shown in some studies, perhaps
due to the glioma-CpG island methylated phenotype (G-CIMP
phenotype) that they represent (50).
BRAF FUSIONS AND MUTATIONS
BRAF is a member of RAS/RAF/MEK/ERK protein kinase
pathway. It plays a key regulatory role in cellular proliferation
and cell survival (51). The most widely known BRAF muta-
tion was initially reported in melanomas as point mutation
(BRAFV600E), but it has now been recognized of impor-
tance in papillary thyroid cancer, colorectal cancer, hairy
cell leukemia, and in gliomas. BRAF alterations are found
in approximately 85% of pediatric low grade gliomas (52).
KIAA1549-BRAF fusion has been reported in 59-90% pilo-
cytic astrocytomas (PAs) especially in the posterior fossa and
is now increasingly being utilized as a diagnostic marker for
PAs where pathological diagnosis is difficult (53,54). Other
fusion partners with BRAF have also been described, but are
much less commonly seen. Point mutation in BRAF V600E
has been reported in up to 80% cases of pleomorphic xanth-
oastrocytoma and 20% of gangliogliomas (55,56). Some
pediatric diffuse astrocytomas may also harbor BRAFV600E
mutations (57). Targeted molecular therapies affecting MAPK
pathway have revolutionized the treatment of melanoma.
Similar therapies are now being investigated in pediatric
clinical trials (58).
HISTONE H3 K27M MUTATION
A new group of mutations involving histones was recently
described in high grade gliomas. Initially found in diffuse
intrinsic pontine gliomas, these mutations have now been
identified in both pediatric and adult gliomas (59). HIST1H3B
and H3F3A are the genes of interest that both encode
histone H3 protein variants: H3.1 and H3.3, respectively.
The two common mutations identified show preference for
tumor location with K27M-mutants often seen in midline
tumors (thalamus, pons, and spinal cord) and G34R/V-mu-
tants seen in hemispheric tumors. The K27M mutation leads
to altered post-translational modification of histone H3
causing impaired DNA methylation that is thought to drive
gliomagenesis (60-62).
With the discovery of this group of mutations, the updated
WHO Classification of Tumours of the Central Nervous System
included a new entity named “diffuse midline glioma, H3
K27M-mutant.” This follows suite with the new trend of an
integrated histologic and molecular diagnosis as this tumor
can only be diagnosed in the presence of a K27M muta-
tion63. In fact, a recent series of 47 infiltrative gliomas found
H3 K27 mutations in multiple midline locations in both chil-
dren and adults, but all with varying histologic appearances.
Tumors ranged from classic lower grade infiltrating astrocy-
tomas to glioblastomas (GBMs) with variants including giant
cell GBM, epithelioid GBM, rhabdoid GBM, GBM with PNET-
like foci, and gliosarcoma. One tumor was even histologically
classified as a pilomyxoid astrocytoma (64).
The wide variation in histologies found to harbor H3 K27M
mutations makes it imperative for us to have the ability
to test for this mutation in pediatric and adult gliomas. A
mutant-specific antibody that detects K27M mutations in
both H3.1 and H3.3 is now widely accepted as a surrogate
for molecular testing. Many groups have published using
this antibody and suggest liberal application for all midline
[CLINICAL RELEVANCE OF MOLECULAR MARKERS IN GLIOMAS - Varun Monga, MBBS, et al]