WHO Grading System

The World Health Organization (WHO) classifies brain tumours by cell origin and how the cells behave, from least to most aggressive. Some tumour types are assigned a grade to signify their rate of growth and to help predict behaviour.

Many non-malignant brain tumours are classified as Grade I or II and malignant tumours as Grade III or IV; however, mixed-grade tumours are possible.

The distinction between non-malignant and malignant tumours can be challenging. Some non-malignant (or low-grade) tumours can be as serious as those classified as malignant (high-grade) if they are in an inaccessible location, such as the brainstem. Conversely, some malignant tumours can be successfully treated. 

WHO Tumour Grading System

Grade I

(Low-grade)

  • Slow-growing cells
  • Cells appear almost normal under microscope
  • Least malignant / aggressive
  • Usually associated with long-term survival 

Grade II

(Low-grade)

  •  Relatively slow-growing cells
  • Slightly abnormal cell appearance under microscope
  • Can invade nearby healthy tissue
  • Can recur as a higher grade tumour

Grade III

(High-grade)

  •  Actively reproducing abnormal cells
  • Cells appear abnormally under microscope
  • Affects nearby healthy tissue
  • Tumour tends to recur, often becoming a higher grade tumour

Grade IV

(High-grade)

  •  Abnormal cells that reproduce rapidly
  • Very abnormal cell appearance under microscope
  • Form new blood vessels to maintain rapid growth
  • Areas of dead cells in centre (necrosis)
Update: In 2016, the World Health Organization (WHO) made changes to it's classification of brain tumours. Read this Ask The Expert article which explains some of the changes and how this affects the diagnosis and management of brain tumours.
Share This

Featured Story

Make every brain tumour count

Stephanie, a 38-year-old mother of twins has been diagnosed with an extremely rare and inoperable brain tumour - a rosette-forming glioneuronal tumour, a type of tumour that little is known about and cannot be removed due to its location in her brain. This reality does not stop Stephanie from her tireless efforts to reduce the stigma of having a brain tumour. Learn why Stephanie is urging all Canadians to make every brain tumour count.

Learn more

Spotlight

Piper's Story: a dream more precious than Olympic gold

Hi, I am Piper Gilles. You may know me as a world-famous ice dancer. I competed in the PyeongChang 2018 Olympic Winter Games. I am a 7...

Learn more

Doug's Adventure

I am Doug, I have brain cancer; I am told it is terminal, but the “good” kind of terminal. I can assure you that receiving that news...

Learn more

Upcoming Events

  • 17/Jul/2019: Niagara Region Support Group: Meets at Wellspring Niagara, 3250 Schmon Parkway, Thorold, ON, L2V 4Y6... Learn more >
  • 18/Jul/2019: Virtual Support Group East: Virtual Support Group for Eastern Canada... Learn more >
  • 20/Jul/2019: Rebounders - LdnOnt: First Baptist Church, 568 Richmond St, London, ON... Learn more >
  • 20/Jul/2019: BrainWAVE ON 2019 Toronto Football: BMO Field Exhibition Place, Toronto, ON... Learn more >
View All Events >
Thank you to the donors whose contributions make this website and all programs, services and research possible.

Copyright © 2019 Brain Tumour Foundation of Canada. Charitable Registration #BN118816339RR0001