Brain tumours are the most common solid tumour in children under the age of 15.
When discovered early enough, brain tumours are usually treatable. Many that are slow-growing are cured with surgery alone. Other types that are faster-growing might need additional treatment with radiation therapy or chemotherapy, or both.
Brain tumours are graded on a scale of 1 to 4, based on how malignant, or cancerous, they are – that is, how abnormal their cells appear under a microscope.
A grade of 1 is the least malignant, and 4 is the most malignant.
A tumour may contain cells of different grades, but it is classified by its highest-grade cells.
The purpose of the brain tumour grading system is to indicate the tumour’s likely growth rate and how likely it is to spread within the brain– information used in predicting outcomes and treatment planning.
Brain tumours are graded and classified by the World Health Organization (WHO).
Grades are often assigned to gliomas, which are tumours that develop in the supporting glial cells of the brain or spine. Gliomas make up about 30% of all brain and central nervous system tumours, and about 80% of all malignant brain tumours.
The most common malignant brain tumours are glioblastomas.
Astrocytomas form from star-shaped brain cells called astrocytes. They are usually noncancerous, slow-growing tumours in children. They commonly develop in children ages 5 to 8. Also called low-grade gliomas, these are the most common brain tumors in children.
Medulloblastomas or Primitive Neuroectodermal Tumors (PNETs) are cancerous, high-grade tumors that start in the posterior fossa, a part of the brain near the base of the skull and are the most common type of childhood brain cancer. Most medulloblastomas occur before age 10.
Ependymomas are a type of childhood brain tumour that form from part of the central nervous system called the ependyma and can be benign (noncancerous) or malignant (cancerous). The location and type of ependymoma determine the type of therapy needed to control the tumor.
Brainstem Gliomas are very rare tumours that form in the tissue of the brainstem, the part of the brain that connects to the spine, and occur almost only in children. The average age at which they develop is about 6. The tumour may grow very large before causing symptoms.
Low-Grade vs. High-Grade
Usually, low-grade tumours are slow-growing, while high-grade tumors are fast-growing and can be cancerous.
High-grade tumors can invade nearby tissue or spread to other areas in the body (metastasise), and they are more likely to come back after treatment to remove them. High-grade tumors are generally associated with a poorer outlook.
Grading of Gliomas
Gliomas classified as grades 1 and 2 are termed low-grade, because their cells are well-differentiated, exhibit less aggressive tendencies and have a better prognosis. Grade 3 and 4 gliomas are considered high-grade: their cells are undifferentiated and highly malignant, and have a worse prognosis.
Grade 1 Tumours are usually associated with long-term survival and are most common in children. They grow slowly and look almost normal under a microscope. Grade 1 tumours often do not need additional therapy after surgery. An example of a grade I tumour is Pilocytic Astrocytoma.
Grade 2 Tumours are relatively slow-growing. Some of them can spread into nearby normal tissue and can transform into a higher-grade tumour. Grade 2 tumours may or may not require additional therapy after surgery. An example is a Grade 2 Astrocytoma.
Grade 3 Tumours are by definition are malignant because they actively reproduce abnormal cells that invade nearby tissue. They tend to recur, potentially as a grade 3 or grade 4 tumour. Grade 3 and 4 tumours always require additional therapy after surgery that typically involves radiation and chemotherapy. An example of a grade 3 tumour is an Anaplastic Astrocytoma.
Grade 4 Tumours are the most malignant and aggressive brain tumours. Their cells are highly abnormal when viewed under a microscope. They recruit new blood vessels to maintain their rapid growth. Glioblastoma is the most common grade 4 brain tumour.