What is Brain Cancer?
Brain cancer is a disease where abnormal cells grow in or around the brain, forming tumours that interfere with normal brain function.
Overview
Brain tumours are either primary, meaning they begin in the brain, or metastatic, meaning they spread to the brain from cancer elsewhere in the body. They can be benign or malignant. Benign tumours, such as pituitary tumours, are not cancerous and often treatable with surgery, though they can still be dangerous because the skull cannot expand, and even non-cancerous growths may press on or damage brain tissue. Malignant tumours, including astrocytomas, oligodendrogliomas and glioblastomas, are cancerous and vary greatly in how they grow and respond to treatment.
Benign vs Malignant
Malignant
Malignant brain tumours are cancers of the central nervous system that arise from brain tissue or supporting glial cells.
They differ from benign tumours in that they grow more aggressively, diffusely infiltrate surrounding brain tissue, and can recur despite treatment.
According to the World Health Organization (WHO), the main types are: astrocytomas, oligodendrogliomas and glioblastomas (GBM).
Benign
Benign brain tumours are classified separately from malignant brain cancers because they usually grow slowly, often have distinct borders, and do not metastasize outside the central nervous system.
Despite these features, they can still be dangerous. A tumour inside the skull can press on or damage vital brain tissue, and depending on its size and location, may become life-threatening.
The most common benign types are meningiomas (most are benign, though 15–20 percent are atypical or malignant), pituitary adenomas (almost always benign; pituitary carcinoma is extremely rare), and vestibular schwannomas (tumours of cranial nerves that are typically benign).
Primary and Secondary Brain Cancer
There are two basic kinds of brain tumours – primary brain tumours and secondary (metastatic) brain tumours.
Primary Brain Tumours
A tumour that starts in the brain is a primary brain tumour.
Secondary or Metastatic Brain Tumours
Secondary brain tumours, also known as brain metastases, are the most common tumours found in the brain in adults.
They usually spread through the bloodstream from a cancer that began elsewhere in the body.
The cancers most likely to spread to the brain are lung, breast, melanoma, kidney, and colorectal cancers. A metastasis keeps the name of the original cancer. For example, colorectal cancer that has spread to the brain is called metastatic colorectal cancer.
There are over 130 types of brain cancer, each with unique genetic mutations, biological behaviours, and treatment approaches.
Common types are gliomas (such as astrocytomas and glioblastomas), meningiomas, medulloblastomas, and metastatic brain tumours. Understanding the specific tumour type is crucial for accurate diagnosis and effective treatment planning.
Brain cancer can cause a wide range of signs and symptoms, depending on the tumour’s type, size, and location in the brain.
Common warning signs include persistent headaches, seizures, changes in vision or speech, and difficulties with balance, memory, or movement. Recognising these symptoms early supports timely diagnosis and care planning.
Doctors classify brain tumours by their grade, which reflects how the tumour cells look under the microscope and how aggressive the tumour is likely to be.
Pathologists assign these grades based on four main features:
- Nuclear atypia (how abnormal the cells look)
- Mitotic activity (how often cells are dividing)
- Microvascular proliferation (growth of new blood vessels)
- Necrosis (areas of dead tissue).
Grades 1–2 are called low-grade tumours, which usually grow slowly. Grades 3–4 are high-grade tumours, which are more aggressive and more likely to recur.
The World Health Organization (WHO) system is the international standard.
Grade 1
- Slow-growing tumours
- Usually not malignant
- Can sometimes be cured with surgery
Grade 2
- Relatively slow-growing tumours
- May infiltrate nearby brain tissue and return after treatment
Grade 3
- Malignant tumours
- Abnormal appearance under a microscope
- Often recur
Grade 4
- Most aggressive tumours
- Grow and spread quickly, often with new blood vessel growth and areas of necrosis (dead tissue)
Researchers do not yet know what causes most brain tumours.
In scientific studies, these factors are described as risk modifiers. A risk modifier changes the likelihood of developing a tumour but is not a direct cause.
Having a risk modifier does not mean someone will definitely develop brain cancer.
Whether you’re facing a new diagnosis or supporting a loved one, help is available. Click here to explore a range of support resources, services, and guidance to assist you through every step of the brain cancer journey.