Understanding Brain Tumours

Brain tumours are quite complex – at present, over 130 different types of ‘high grade’ (cancerous) or ‘low grade’ (non-cancerous) brain tumours are known.

What is a brain tumour?

A brain tumour occurs as a result of an abnormal growth or spread of cells from within the brain or its supporting tissues that can damage the brain or threaten its function.

Some types of tumour can occur around the edge of the brain and press on certain parts of it, whilst others can be more diffuse, spreading out and growing in amongst healthy brain tissue.

Brain tumours are divided into four classifications – grades I (1) and II (2) are low-grade, grades III (3) and IV (4) are classed as high-grade. High-grade or malignant brain tumours are aggressive and can spread quickly in the brain, and are usually a serious threat to life. Low-grade or benign brain tumours are slower-growing and not usually immediately life threatening, but can still have a potentially dangerous impact on a person’s well-being.

What causes a brain tumour?

The direct cause of a brain tumour is still not clear, so more investment in research is urgently needed. There are over 120 different types of brain tumour.

What is the prognosis of a brain tumour?

The prognosis – impact on well-being and threat to life – is mainly dependent on type of tumour, location in the brain, tumour size at time of diagnosis, growth and how much can be removed or successfully treated. Factors including the patient’s age and general health also have bearing, as well as some recognised genetic factors.

What’s the difference between primary and secondary brain tumours?

Approximately 16,000 people are diagnosed with a brain tumour in the UK every year and there are estimated to be about 60,000 people living with a brain tumour.

A primary brain tumour is one that has originated in the brain, whether low-grade or high-grade.

A secondary brain tumour, also known as a metastatic brain tumour, is one that has developed from a type of cancer that began in another part of the body and then spread (metastasised) to the brain. They occur as a result of certain types of cancer cells from cancers in other parts of the body being carried in the blood to the brain, where they stick and then grow into a new tumour.

The most common types of cancer that can spread to the brain are lung, breast, and melanoma (a type of skin cancer) with other cancers able to as well.

What is a low-grade brain tumour?

A low-grade tumour is normally classified as a Grade I or Grade II brain tumour, according to the World Health Organisation (WHO) classification guidelines.

Grade I tumours tend to occur in children and young adults but are usually well treated and carry a good prognosis.  Some Grade I tumours may just need surgery, not radiotherapy or chemotherapy. They may re-grow at a slow rate, and further treatment may be possible to reduce their size again. Regular monitoring and careful management is likely to be recommended by the patient’s clinical team.

Grade II tumours carry the risk that they will eventually transform into higher grade tumours. Some tumours initially classified as Grade II tumours may harbour altered genes that make them behave like high-grade tumours, hence they may need early biopsy or surgery.

A low-grade brain tumour is slow-growing, compared to a high-grade tumour. It may not come back if it is completely removed by surgery, but recurrence and transformation to a higher grade often occurs. The tumour’s position in the brain will determine if surgery is possible or not.

Low and high-grade brain tumours rarely spread outside the central nervous system, but can grow into brain or spread at a distance within the brain tissue to form other areas of growth.

What is a high-grade brain tumour?

These brain tumours are classified as grade III or grade IV. They are fast-growing, aggressive in behaviour and life-threatening.

A high-grade brain tumour usually comes back after treatment, even if it appears to have been completely eradicated the first time. This is because of its invasive nature; the ability to spread its tumour-forming cells to other parts of the brain or spinal cord.

How are brain tumours graded or classified?

Pathological Classification of a person’s brain tumour enables a clinician to determine the best course of action in treating a patient’s tumour after diagnosis.

The World Health Organisation (WHO) issues updates to the global guidelines for the classification of brain tumours every few years. Current WHO guidelines were last updated in 2016 to include DNA (genetic) profiling of brain tumours as well as the traditional histology – the examination of tumour cells under the microscope.

Tissue samples are required for classification and are obtained by a neurosurgeon performing a biopsy or removal (resection) of the tumour. Samples are sent to pathology labs for careful scientific classification of the tumour.

What is a calcified brain tumour? What is a brain tumour cyst? And what is brain tumour necrosis?

While more unusual, read on to find useful information on these three areas of brain tumours.


​Find key information about brain tumours in adults and children including symptoms, diagnosis and treatments, and read advice on living with, or caring someone with, a brain tumour.