Grades of Brain Cancer
Brain cancer grading is a system that classifies tumours based on how the cancer cells look under a microscope, how fast the tumour is growing, and how likely it is to invade nearby healthy brain tissue.
What is brain cancer grading?
The brain cancer grading system is defined by the World Health Organization (WHO) and is part of its internationally recognised classification framework, which ensures consistency in diagnosis and reporting. The WHO assigns tumour grade based on how abnormal the tumour cells appear compared with healthy cells, their potential to spread into surrounding brain regions, and key molecular characteristics that influence tumour behaviour. Tumour grading helps guide treatment decisions and provides information about expected tumour behaviour, although it is only one part of the overall clinical picture.
Grading vs Staging
Brain tumour grading is different from cancer staging used for cancers in other parts of the body. Cancers such as lung, breast, or skin cancer are staged based on how far they have spread throughout the body. Brain tumours are graded rather than staged because they rarely spread outside the central nervous system.
The 4 Brain Cancer Grades (Grade 1 → Grade 4)
For many brain tumours, grading allows your healthcare team to understand how aggressive a tumour is and how it is likely to behave over time. This information supports doctors in choosing the most appropriate treatment for each individual. Below is a general overview of how tumour grades are commonly described.
Grade 1 tumours are usually slow-growing and are often considered as low-grade tumours. They are typically well-defined and less likely to invade surrounding brain tissue. In many cases, surgery alone may be sufficient, and long-term outcomes are often favourable. However, ongoing follow-up is still important.
Grade 2 tumours are also considered low-grade but tend to grow slowly over time rather than remaining stable. Unlike Grade 1 tumours, they can grow into nearby brain tissue and may progress to higher-grade tumours over time. Regular monitoring and, in some cases, additional treatment may be required.
Grade 3 tumours are malignant and grow more quickly. The tumour cells appear more abnormal under the microscope and are more likely to spread into surrounding areas of the brain. Treatment often involves a combination of therapies.
Grade 4 tumours are the most aggressive and malignant. The tumour cells appear highly abnormal and tend to grow rapidly and infiltrate surrounding brain tissue. These tumours usually require prompt treatment using multiple approaches.
Low-grade vs High-grade: What’s the difference?
Low-grade tumours are generally classified as Grades 1 and 2. They tend to grow more slowly and may behave less aggressively than higher-grade tumours. Some low-grade tumours have more well-defined borders, which can make surgical removal easier, while some may invade nearby tissue and require long-term monitoring.
While Grade 1 tumours are typically less aggressive and may only require surgery and follow up, Grade 2 tumours carry a higher risk of progression over time and may require additional treatment.
High-grade tumours are generally classified as Grades 3 and 4. These tumours are more aggressive, grow more rapidly, and can infiltrate nearby brain tissue. Because of this infiltrative behaviour, treatment often involves a combination of approaches, such as surgery followed by radiotherapy and chemotherapy.
High-grade tumours also have a higher risk of recurrence after treatment. This may occur because some tumour cells survive treatment, because tumours contain a mix of cells that respond differently to therapy, or because complete surgical removal is not always possible without risking damage to important brain tissue. As a result, outcomes for high-grade tumours are generally less favourable compared with low-grade tumours, which often have better long-term outcomes.
How brain cancer grading influences treatment planning
Brain tumour grading plays an important role in guiding treatment decisions including the type and intensity of therapy. Low-grade tumours, particularly Grade 1 tumours, tend to grow slowly and may be managed with close monitoring or surgery alone, depending on symptoms and tumour behaviour. Because these tumours have a lower risk of rapid progression, they may be followed over a longer period with regular imaging to watch for changes.
High-grade tumours generally require a more urgent and intensive treatment approach. Patients with high-grade tumours are usually monitored more closely, with frequent follow-up appointments and MRI scans. Treatment plans may be adjusted over time, especially if the tumour does not respond as expected or shows signs of progression
High-grade tumours often contain a mixture of tumour cells, some of which may respond to treatment while others do not. This variability can make treatment more challenging and is one reason why care plans are tailored to each individual. In addition to tumour grade, modern treatment planning increasingly uses molecular markers found within the tumour to help predict how it may respond to treatments such as chemotherapy and radiotherapy.
Why and how tumours can change grade over time
Despite a lower risk of aggressive behaviour, low-grade tumours, particularly Grade 2 tumours, can sometimes change and become higher grade over time. This process, known as tumour progression may happen as tumour cells gradually acquire additional genetic changes that allow them to grow more aggressively. In some cases, a small number of tumour cells may survive initial treatment and later multiply, leading to tumour regrowth.
When progression is suspected, your healthcare team may adjust your follow-up plan by scheduling more frequent appointments and imaging scans to closely monitor how the tumour is changing. Careful monitoring allows your team to adapt the treatment approach as the tumour evolves.
It is also important to understand that specific genetic changes within the tumour, identified through molecular testing, can influence treatment decisions and help guide prognosis. For example, if a low-grade tumour progresses to a higher grade, molecular testing may detect new genetic alterations even when the tumour appears similar under the microscope. If there is concern that the tumour’s behaviour has changed, your healthcare team may recommend further testing, and in selected situations, a repeat biopsy to better understand the tumour and guide future treatment.
References
Porter, A. B., Wen, P. Y., & Polley, M.-Y. C. (2023, 2023/05/01). Molecular Profiling in Neuro-Oncology: Where We Are, Where We’re Heading, and How We Ensure Everyone Can Come Along. American Society of Clinical Oncology Educational Book(43), e389322. https://doi.org/10.1200/EDBK_389322
Ullah, F., Nadeem, M., Abrar, M., Amin, F., Salam, A., Alabrah, A., & AlSalman, H. (2023). Evolutionary Model for Brain Cancer-Grading and Classification. IEEE Access, 11, 126182-126194. https://doi.org/10.1109/ACCESS.2023.3330919
Uzun Ozsahin, D., Denker, A., Kibarer, A. G., & Kaba, S. (2021). Chapter 4 – Evaluation of stage IV brain cancer treatment techniques. In I. Ozsahin, D. U. Ozsahin, & B. Uzun (Eds.), Applications of Multi-Criteria Decision-Making Theories in Healthcare and Biomedical Engineering (pp. 59-69). Academic Press. https://doi.org/10.1016/B978-0-12-824086-1.00004-9