Medulloblastoma (muh-dul-o-blas-TOE-muh) is a cancerous, also called malignant, brain tumor that starts in the back and lower part of the brain.
This part of the brain is called the cerebellum. The cerebellum helps control balance, movement and coordination.
Medulloblastoma is the most common cancerous brain tumor in children, though it also can happen in adults.
Medulloblastoma forms when cells in the cerebellum develop changes in their DNA. These changes cause the cells to grow and multiply quickly. The tumor can press on nearby parts of the brain and may block the flow of cerebrospinal fluid. This can cause pressure to build up in the brain.
Medulloblastoma can spread, also known as metastasize, to other parts of the brain and spinal cord through cerebrospinal fluid. It rarely spreads outside the central nervous system.
There are four main types, also called molecular groups, of medulloblastoma. These groups are defined by the tumor’s genetic features. The four groups are WNT-activated, SHH-activated (including TP53-mutant and TP53-wildtype), group 3 and group 4.
Group 3 and group 4 tumors are sometimes described together as non-WNT and non-SHH tumors, although they are separate groups. Knowing the tumor type helps guide treatment.
Hearing this diagnosis can feel overwhelming. It may help to know that, with treatment, many children with medulloblastoma live well beyond five years after diagnosis.
Every child's situation is different. The outlook depends on several factors, including age, tumor type, whether the cancer has spread and how much of the tumor can be safely removed.
The type of medulloblastoma is based on how the tumor cells look under a microscope and on lab tests that look at changes in the tumor's genes. The type of medulloblastoma helps guide treatment and can affect survival.
All medulloblastomas are considered grade 4 tumors. The subtypes below describe the tumor's molecular features, not its grade.
Molecular types
Most medulloblastomas can be grouped into four main types based on changes in their genes. These tumor types include:
-
WNT-activated (wingless/integrated). WNT is the name of a cell signaling pathway involved in brain development. WNT-activated tumors are one of the less common medulloblastoma types. They often respond very well to treatment and are linked to the best survival rates. They are most often seen in older children and teens.
-
SHH-activated (sonic hedgehog). Sonic hedgehog is the name of a cell growth signaling pathway involved in brain development. SHH medulloblastoma can occur in infants, children and adults. Survival varies depending on other tumor features and gene changes. Some SHH tumors, known as SHH-activated TP53-wildtype, behave less aggressively. Other SHH tumors, called SHH-activated TP53-mutant, may be harder to treat.
-
Group 3. Group 3 medulloblastoma is more common in young children. These tumors are non-SHH and non-WNT molecular types. It tends to grow and spread more quickly than other types. It may be harder to treat and is often linked to lower survival rates compared with WNT tumors.
-
Group 4. Group 4 medulloblastoma is the most common type. These tumors are non-SHH and non-WNT molecular types. It can occur in children and adults. Its behavior varies. Some tumors respond well to treatment, while others may spread at diagnosis.
The numbering starts at 3 and 4 because the first two groups were named WNT-activated and SHH-activated based on specific gene patterns.
Cell appearance types
Medulloblastoma also can be described based on how the cells look under a microscope although genetic and molecular features are increasingly used for diagnosis and understanding outcomes. These include:
- Classic.
- Desmoplastic or nodular.
- Large cell or anaplastic.
These features also help healthcare professionals understand how the tumor may behave.
How is medulloblastoma different from other brain tumors?
Medulloblastoma is different from many other types of brain tumors. These tumors differ in where they start, who they affect and how they are treated.
Here's how they compare:
-
Medulloblastoma versus glioma. Medulloblastoma is not a glioma. Gliomas form from support cells in the brain called glial cells. Medulloblastoma forms from developing nerve cells in the cerebellum.
-
Medulloblastoma versus glioblastoma. Glioblastoma is an aggressive brain tumor that usually affects adults and starts in the upper parts of the brain. Medulloblastoma is more common in children and often responds better to treatment.
-
Medulloblastoma versus ependymoma. Ependymomas begin in cells that line the fluid-filled spaces of the brain and spinal cord. Medulloblastoma tends to grow in the cerebellum and is more likely to spread through cerebrospinal fluid.