Understanding brain cancer grading

What is brain tumour grading?

The brain tumour grading system is the process doctors use to classify a brain tumour based on how abnormal its cells appear under a microscope, and how quickly they are likely to grow and spread within the central nervous system (including the brain or spinal cord). The World Health Organisation (WHO) recommends a grading system with four distinct grades for both benign and malignant brain tumours. This systematic approach, together with staging systems such as TNM (Tumour, Node, Metastasis), provides a complete, standardised picture of your diagnosis and the biological behaviour of your tumour.

Doctors gather grading and staging information from a physical exam, your medical history, imaging tests like magnetic resonance imaging (MRI), CT scan, and sometimes a PET scan or lumbar puncture. A biopsy sample, obtained through open biopsy or needle biopsy, provides detailed information on tumour cells, the presence of cancer cells, and the specific tumour type, including rare tumours and common primary brain tumours like astrocytomas, oligodendrogliomas, and tumours that arise from glial cells, nerve cells, or germ cells.

The TNM staging system explained

While grading is the primary system for classifying primary brain tumours and malignant primary brain tumours, the TNM staging system is also sometimes used, especially in clinical oncology for metastatic brain tumours (secondary brain tumours that result from cancer elsewhere in the body). The staging system includes:

• T (Tumour): Size, location, and part of the brain or spinal cord affected by the primary tumour, and whether tumours develop in nearby tissues.
• N (Nodes): Lymph node involvement (rare in primary brain tumours, but important in metastatic cancer and certain tumour types).
• M (Metastasis): Whether cancer cells have spread outside the brain or spinal cord, including metastatic brain tumours and secondary tumours.

Staging and grading work together to provide health professionals and patients with a detailed understanding of the disease and the best treatment plan.

Understanding the WHO grading system

The World Health Organisation (WHO) grading system assigns brain tumours to one of four grades, from the least aggressive (low grade) to the most aggressive (grade 4 brain cancer, or high grade), helping patients and their care teams understand tumour behaviour and expected disease progression.

Grade 1: low-grade tumour

A Grade 1 benign brain tumour contains slow-growing, abnormal cells that look very similar to normal cells (including healthy cells like those that support nerve cells and brain health). These tumours are typically well-defined, may affect children or adults, and are considered non-cancerous. When completely removed surgically (complete surgical removal), grade 1 tumours offer an excellent prognosis and rarely spread to nearby brain tissue.

Grade 2: low-grade tumour

A Grade 2 primary brain tumour is still slow growing, but its abnormal cells look slightly more atypical than Grade 1. These common form tumours can invade nearby tissue and can transform into higher grade tumors (disease progression). Examples include low-grade gliomas and certain rare tumours. Complete surgical removal may be more challenging, but careful monitoring helps track signs and symptoms or new symptoms.

Grade 3: high-grade tumour

Grade 3 brain tumours are considered malignant brain tumours, a more aggressive type of tumour with a higher risk of recurrence. Tumour cells appear very different from normal cells, invade healthy brain tissue or nearby tissues, and grow rapidly, often causing significant symptoms and impacting bodily functions, memory loss, or other symptoms depending on the parts of the brain or cranial nerves affected.

Treatment options for grade 3 tumours include surgery, radiation therapy (using techniques such as stereotactic radiosurgery, gamma rays, or proton therapy to deliver high doses and kill cancer cells), chemotherapy, and sometimes clinical trials investigating new medications. Regular scans and support from your healthcare team or rehabilitation specialists are essential for monitoring treatment response and the next review.

Grade 4: high-grade tumour

Grade 4 brain tumours, such as glioblastoma multiforme, malignant gliomas, or metastatic brain tumours, contain cancerous cells that divide rapidly, invade healthy cells and blood vessels, and may cause brain metastases. These aggressive tumours often cause common symptoms like headaches, neurological changes, and may rapidly affect the brain and spinal cord, cerebrospinal fluid, and other brain tumours.

Grade 4 brain tumours, also called malignant brain tumours, present unique challenges. Treatment involves a multidisciplinary team, including health professionals and emotional support specialists, to provide surgery, high-dose radiation, clinical trials, and palliative care to manage symptoms and maintain quality of life.

Tumour type and treatment planning

Your treatment plan is shaped not only by the tumour’s grading and type, but also by factors like your overall health, the part of the brain or spinal cord affected, types of brain tumour (including common brain tumour types and primary tumours), and whether the tumour affects the central nervous system, brain stem, cranial nerves, or germ cell tumours such as pineal tumour or pituitary tumours. Common primary brain tumours occur in adults and children, while rare tumours and secondary brain tumours can develop in a broader range of ages.

The molecular profile of tumour types (including specific tumour grade and genetic mutations) further tailors your treatment options, such as surgery, radiation therapy, targeted therapy, palliative care, or support for slow-growing tumours and benign tumours.

The role of imaging tests in assessment

Imaging plays a central role: magnetic resonance imaging (including functional MRI, magnetic resonance spectroscopy, and MR perfusion), CT scan, and X-rays create pictures and detailed images of tumours, allowing healthcare providers to assess size, location, and involvement of parts of the brain. PET scan, radio waves, and strong magnets help provide additional detailed information about blood flow, nervous system function, and the relationship with nearby tissue.

Imaging also aids in differentiating benign tumours from malignant brain tumours, stage 4 brain cancer, and mapping treatment for the brain. It helps plan the best treatment plan and monitor for disease progression.

Living with a high-grade brain tumour

Living with a high-grade brain tumour or metastatic brain tumours often means ongoing care with a multidisciplinary team. Treatments may include repeated imaging, palliative care to manage significant symptoms and scalp irritation, and rehabilitation for vision loss, muscle strength, and other symptoms affecting normal development or nervous system function.

Support is available for patients and families from organisations like the Central Brain Tumour Registry and the National Brain Tumour Society, as well as healthcare professional networks offering guidance about half of all patients who develop or are diagnosed with a brain or spinal cord tumour.