The newly announced Brain Tumour Research Centre of Excellence at The Institute of Cancer Research is making these devastating childhood tumours its research focus.
What are gliomas?
Gliomas are the most common central nervous system (CNS) tumours in children and adolescents, and they show an extremely broad range of clinical behaviour and can be high-grade (malignant) or low-grade (non-malignant). They form from what are known as precursor or progenitor cells, which during normal brain development go on to form either the neurons or the non-neuronal support cells of the CNS known as glial cells. Glial cells are made up of a variety of cell types, such as astrocytes, oligodendrocytes and ependymal cells, all of which have a large number of essential roles in maintenance and function of the CNS.
Historically, paediatric gliomas have been both grouped with adult gliomas, i.e., paediatric glioblastoma, and separate to adult gliomas, i.e., diffuse pontine intrinsic glioma. However, there is now a lot of literature confirming that paediatric gliomas have different molecular pathological features from adult glioblastomas, therefore in the new WHO 2021 CNS Tumour Classification paediatric gliomas are classified separately from adult gliomas and are divided into low-grade (1-2) and high-grade (3-4) groups.
Paediatric high-grade gliomas are now classified as “Paediatric-type diffuse high-grade gliomas” and include:
- Diffuse midline glioma, H3 K27-altered
- Diffuse hemispheric glioma, H3 G34-mutant
- Diffuse paediatric-type high-grade glioma, H3-wildtype and IDH-wildtype
- Infant-type hemispheric glioma
Each of these high-grade gliomas are distinct from one another and, as such, have different features and prognosis. See below for detailed information on each glioma type.
Diffuse midline glioma (H3 K27-altered)
Diffuse midline glioma (DMG) tumours are found in the midline of the brain which includes structures such as spinal cord, thalamus and brainstem.
The majority of DMGs are found in young children and are located in the pons in the brainstem. Until recently, those in the pons were called diffuse intrinsic pontine gliomas (DIPG), however, they are now considered within the category of DMG.
Those seen elsewhere in the midline, other than the pons, tend to be in children and young adults, particularly spinal cord tumours, which are primarily seen in young adults.
These tumours are also defined by highly specific mutations in a gene which produces histone H3 – a critical protein around which DNA is wrapped – that are unique to these tumours.
Prognosis for these tumours remain poor, with a two-year survival of less than 10%.
It is important to note that some tumours can be called brainstem gliomas, and while these are usually referring to diffuse midline gliomas, there are other brainstem glioma tumours, such as ganglioglioma or pilocytic astrocytoma, which are not part of the paediatric-type diffuse high-grade glioma classification.
Diffuse hemispheric glioma (H3 G34-mutant)
Diffuse hemispheric gliomas are rare, high-grade, infiltrating tumours that generally occur in adolescents and young adults. The tumours are usually found in the cerebral hemispheres, mainly in temporal and parietal lobes.
Similarly to DMG, these tumours are also defined by highly specific mutations in a gene which produces histone H3, that are unique to these tumours.
Diffuse hemispheric gliomas carry a poor prognosis with a median survival of 18-22 months. Treatment is surgical removal, followed by radiotherapy and chemotherapy.
Diffuse paediatric-type high-grade glioma (H3-wildtype and IDH-wildtype)
Diffuse paediatric-type high-grade gliomas were historically referred to as paediatric glioblastoma and exhibit glioblastoma-like features. The vast majority are found in the cerebral hemispheres.
Treatment of these tumours consists of total (ideally) or near total surgical removal, followed by radiotherapy and chemotherapy. They usually have a poor prognosis with a median survival of 17.2 months , but this can differ depending on the subtype of the tumour, of which there are at least three.
Infant-type hemispheric glioma
Infant-type hemispheric gliomas, also known as infant high-grade gliomas, typically arise in infants from birth-12 months. They are found in the cerebral hemispheres and have distinct mutations than that of other paediatric high-grade gliomas.
They tend to have a better overall survival than other paediatric-type diffuse high-grade gliomas, with a five-year overall survival of 54.5%.
There have been four subtypes identified, which seem to have slightly different overall survival rates, but more information is needed.
References
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Guerreiro Stucklin, A. R. S. F. K. e. a., 2019. Alterations in ALK/ROS1/NTRK/MET drive a group of infantile hemispheric gliomas. Nat Commun, Volume 10.
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