Brain Tumours

What are brain tumours?

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 1 and 2 are low-grade, grades 3 and 4 are classed as high-grade. High-grade or malignant brain tumours are aggressive and can spread quickly in the brain, they 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?

No single, definitive cause has yet been identified for primary brain tumours.

Some risk factors have been identified, but due to the complex and unique health history of each patient, scientists are still unable to answer this fundamental question of why a brain tumour has appeared. Like all tumours and cancers, mutations in the DNA of a cell leads to abnormal growth (uncontrolled division), but what causes these mutations is likely to vary between individuals.

Find out more about the causes of a brain tumour

What is the prognosis of a brain tumour?

The prognosis – impact on well-being and threat to life – is dependent on the type of tumour, location in the brain, size at time of diagnosis, growth rate and how much can be surgically removed or successfully treated.

Factors including patient age and general health also have a bearing, as well as some recognised genetic factors.

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

A primary brain tumour is one that has originated in the brain. There are more than 120 different types of brain tumours and they can be low-grade or high-grade. More than 12,000 people are diagnosed with a primary brain tumour in the UK every year and there are estimated to be over 60,000 people living with a brain tumour.


A secondary brain tumour, also known as a metastatic brain tumour, is one that has developed from 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).

Find out more about the different brain tumour types

What is a low-grade brain tumour?

A low-grade tumour is normally classified as a grade 1 or grade 2 brain tumour, according to the World Health Organisation (WHO) classification guidelines.

Grade 1 tumours tend to occur in children and young adults but are usually well treated and carry a good prognosis. Some grade 1 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 are likely to be recommended by the patient’s clinical team.

Grade 2 tumours carry the risk that they will eventually transform into higher-grade tumours. Some tumours initially classified as grade 2 tumours may harbour altered genes that make them behave like high-grade tumours, hence they may need an 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 position of the tumour 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 the 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 3 or Grade 4. 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?

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

Classification of the tumour can be achieved by DNA (genetic) profiling of brain tumours as well as 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.

The World Health Organisation (WHO) issues updates to the global guidelines for the classification of brain tumours every few years. The WHO guidelines were last updated in 2021.

What is a calcified brain tumour?

A calcified brain tumour is one in which calcium has built up. A range of different types of brain tumour can show different patterns and extent of calcification.

Calcification happens when tumours are no longer able to regulate the movement of calcium in and out of their cells. This may be due to damage to the blood vessels, resulting in a localised haemorrhage (uncontrolled blood flow) within the tumour that kills some of the cells. Calcium flow is disrupted even further and calcium builds up around the dead cells, so calcification tends to indicate that portions of the tumour have died (brain tumour necrosis) and are no longer actively growing.

What is brain tumour necrosis?

A necrotic brain tumour means that some cells within the tumour have died, for example in the centre of a glioblastoma multiforme (GBM) brain tumour.

What is a brain tumour cyst?

A brain tumour cyst is a sac or bubble that can form in or near a brain tumour. It may contain some tumour cells, brain or spinal cells, blood, and cerebrospinal fluid (a transport for molecules and waste products between cells and the blood, a lubricant and a shock absorber for the brain and spine).

Cysts can cause similar symptoms to a brain tumour because they place pressure on the surrounding brain, but they are not cancerous in themselves. Cysts are typically removed via surgery to remove and/or drain the cyst.