Brain and Central Nervous System (CNS) tumours form over a quarter of all childhood cancers in the UK, and are the second most common of all, behind Leukaemia. The largest subgroup of these is astrocytoma, which accounts for over two-fifths of all brain and CNS tumours in children. It is a disease which forms in glial cells called astrocytes, which are the most abundant cell of the human brain. Astrocytes perform many functions, including helping in repair and scarring processes. Astrocytoma begins when normal astrocytes change and grow uncontrollably. These then form a glioma, a mass that is more commonly known as a tumour.
Pilocytic Astrocytomas are classified by the World Health Organisation as benign, Grade I, low-grade tumours because they grow relatively slowly and as they are non-invasive, they have clearly defined borders. Low-grade is the classification given to around three-quarters of Astrocytomas.