CNS tumours arise from different types of cells in the brain and are classified according to the cell type and area of the CNS in which they began.
Most CNS tumours start in glial cells – the supporting cells of the brain. These tumours are known as gliomas and include astrocytomas, ependymomas and oligodendrogliomas.
Another group of tumours arise from embryonal cells. These tumours include medulloblastoma and PNET (primitive neuro-ectodermal tumour).
Altogether there are more than 100 different types of brain tumour, most of which are very rare.
Tumours classified as low grade (benign) are very slow growing and remain in the part of the brain in which they started. High grade (malignant) brain tumours are likely to be more aggressive and to spread into the brain tissue which surrounds them. This can cause pressure and damage to the surrounding areas.
Around 400 children are diagnosed with a CNS tumour every year in the UK – a quarter of all childhood cancer cases.
Astrocytoma is the most common type of brain tumour in children, accounting for about 40 per cent of cases (155 children per year in the UK). Around 75 per cent of childhood astrocytomas are low grade.
The second most frequent sub-group are the embryonal tumours which account for around 20 per cent of cases (70 cases per year in the UK). Embryonal tumours are more common in early childhood and more common in boys than girls. Most embryonal CNS tumours are medulloblastomas (around 50 cases per year), with PNETs making up most of the remaining cases (around 16 cases per year).
Ependymomas make up about 10 per cent of childhood CNS tumours.
The overall five-year survival rate for childhood CNS tumours is 75 per cent.
However, this rate varies widely according to the type of tumour, the grade (whether it is benign or malignant), the size, and the site in the brain or spinal cord.
Low-grade astrocytomas, which account for 30 per cent of all childhood CNS tumours, have a survival rate of 95 per cent.
High-grade astrocytomas, however, have a very different prognosis – with five year survival below 20 per cent. A type of tumour called Diffuse Intrinsic Pontine Glioma, DIPG, is considered incurable, with most young patients dying within nine months of diagnosis.
Ependymoma has five-year survival of 71%, medulloblastoma 64% and PNETs just 36%.
CNS tumours claim the lives of 100 children a year in the UK, one third of all childhood cancer deaths.
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