How brain tumours are graded

Brain tumours are graded 1-4 according to their behaviour, such as the speed at which they are growing, and how likely they are to spread into other areas of the brain. Over time, some brain tumour's behaviour can change and the tumour may become, or come back as, a higher grade tumour.

Each year in the UK, approximately 4,300 people are diagnosed with low grade, slow growing brain tumours and 5,000 with high grade fast growing brain tumours. Combined, this represents less than 2 out of every 10,000 people in the UK.

Brain tumours are graded from 1 – 4 depending on how they are likely to behave.

• Grade 1 and 2 tumours (low grade)
• Grade 3 and 4 tumours (high grade)

Confirming the diagnosis of the different grades of brain tumours is done, where possible, by analysing cells from the tumour, taken during a biopsy or during surgery. A neuropathologist examines the cells in the laboratory, looking for particular cell patterns that are characteristic of the different types and grade of brain tumour.

Why is the grade important?

Accurate diagnosis is important as it allows your medical team to give you information about how the tumour could behave in the future, and also to recommend treatment options. This could include a clinical trial.

Sometimes confirming the grade can be difficult as some low grade and high grade tumours can look very similar.

Low grade tumours

Low grade brain tumours are:

• slow growing
• relatively contained with well-defined edges
• unlikely to spread to other parts of the brain
• have less chance returning (if they can be completely removed).

Grade 1 and 2 tumours are low grade, slow growing, relatively contained and unlikely to spread to other parts of the brain. There is also less chance of them returning if they can be completely removed. They are sometimes still referred to as 'benign'.

The term 'benign' is less used nowadays as this can be misleading. These low grade brain tumours can still be serious.

This is because a 'benign' tumour can cause harm by pressing on and damaging nearby areas of the brain, due to the limited space capacity of the skull. They can also block the flow of the cerebrospinal fluid (CSF) that nourishes and protects the brain, causing a build-up of pressure on the brain.

High grade tumours

High grade brain tumours are:

• fast growing
• can be referred to as 'malignant' or 'cancerous' growths
• more likely to spread to other parts of the brain
• may come back, even if intensively treated.

Grade 3 and 4 tumours are high grade, fast growing and can be referred to as 'malignant' or 'cancerous' growths.

They are more likely to spread to other parts of the brain (and, rarely, the spinal cord) and may come back, even if intensively treated. They cannot usually be treated by surgery alone, but often require other treatments, such as radiotherapy and/or chemotherapy.

'Mixed grade' tumours

Some tumours contain a mixture of cells with different grades. The tumour is graded according to the highest grade of cell it contains, even if the majority of it is low grade.