molecular subtypes, which yields a robust nonoverlapping,

clinically relevant classification that is superior to traditional

histologic methods in predicting biological behavior. LGG class

is based on the fluorescence in situ hybridization status of 3

important markers: IDH1, 1p19q (codeletion of both 1p and

19q), and ATRX (α-thalassemia/mental retardation syndrome

X-linked gene).

This molecular classification results in 2 diffusely infiltrating

astrocytomas that are stratified primarily according to IDH1

status. Astrocytomas with a more favorable prognosis exhibit

IDH mutation {are IDH1(+)] &/or ATRX mutation [ATRX(+)].

1p19q is nondeleted. The 2nd group is those that are IDH1(-)

(wild-type). Even though they may appear histologically low

grade (WHO II), wild-type tumors are aggressive neoplasms

that behave more like GBMs. Oligodendrogliomas exhibit

1p19q codeletion and are typically IDH1(+). ATRX is

nonmutated.

O-6-methylguanine-DNA methyltransferase (MGMT)

promoter profiling is important for glioma treatment

stratification. MGMT(+) tumors are typically more

chemosensitive than wild-type neoplasms.

Gliomas in children vs. adults: Pediatric gliomas are often

genetically different from their adult counterparts, even

though they appear identical under the microscope. Intrinsic

pediatric pontine gliomas, aggressive neoplasms that are

almost always fatal, exhibit histone (H3) and ACVR1 mutations.

In contrast to adult oligodendrogliomas, pediatric

oligodendrogliomas rarely exhibit 1p19q codeletion.

Ependymal tumors: Classic histologic criteria divide

ependymal neoplasms into grade I subependymomas or

myxopapillary ependymomas, grade II ependymomas (further

subdivided into cellular, papillary, clear cell, and tanycytic

types), and grade III (anaplastic) ependymomas.

DNA methylation profiling has recently identified 9 molecular

subgroups of ependymoma. This molecular classification

outperforms the current histopathological grading in the risk

stratification of patients for treatment.

Choroid plexus tumors (CPTs): CPTs are papillary

intraventricular neoplasms. Almost 80% are found in children.

Classically, CPTs have been divided into choroid plexus

papillomas (CPP) (WHO grade I), atypical choroid plexus

papillomas (aCPP) (WHO grade III), and choroid plexus

carcinomas (CPCa), designated as WHO grade III. Recent

genomic analysis has shown aCPP is an immature variant of