What is medulloblastoma?

Medulloblastoma is one of the most common paediatric brain cancers [1, 2]. These tumours are found in the cerebellum, the part of the brain located at the lower back of the head near the spinal cord. On average, about 80% of those diagnosed with medulloblastoma will survive their disease [3], but that statistic does not tell the whole story.

Outcomes depend heavily on the type of medulloblastoma a patient has. There are 4 subgroups, each with distinct genetic mechanisms and clinical characteristics [4]. Survival rates for the lowest-risk tumours exceed 90% [5], while some high-risk subtypes show survival rates below 50% [6].

How does medulloblastoma arise?

Despite making up a small fraction of the size of the whole brain, the cerebellum contains about 80% of the brain’s neurons, cells that transmit electrical signals [7]. To produce all these neurons, an incredible amount of cell division occurs in the cerebellum during embryonic development, making these cells particularly vulnerable to transformation into cancer during this period.

Normally, once enough neurons are made, cell division stops. Medulloblastoma arises when cells instead get stuck in growth mode [8-11]. Genetic mutations that they acquire while dividing are usually the cause, but in some cases inherited mutations can contribute to medulloblastoma formation.

How is medulloblastoma diagnosed and treated?

Medulloblastoma is usually detected through imaging with MRI, often after a child has shown neurological symptoms such as abnormal gait (walking), headache, nausea, seizures dizziness, or blurred/double vision [12, 13].

If an medulloblastoma-like tumour is seen on MRI, the first line of treatment is usually to remove as much of it as possible surgically [14]. Surgery also allows the patient’s care team to obtain pieces of the tumour for testing. This helps them confirm whether it is an medulloblastoma, and if so, which subgroup.

The specifics of treatment following surgery depend on medulloblastoma subgroup but most treatment plans involve radiation and chemotherapy [14]. Radiation is often avoided for the youngest patients (usually <3 years) because their still-developing brain is especially vulnerable to its side effects [14], but this makes treating medulloblastoma in very young patients particularly difficult.

Current challenges in medulloblastoma treatment

Traditional cancer therapies like surgery, chemotherapy and radiation continue to dominate care strategies [14, 15]. These therapies can save lives and improve quality of life, but 20% of those diagnosed with medulloblastoma still do not survive their disease.

Standard therapies are also harsh on the body, especially radiation, which can come with significant long term side effects. Medulloblastoma survivors are at higher risk of experiencing hearing loss, infertility, and stroke [16]. They are also more likely to have developmental and learning disabilities correlated with the amount and location of radiation they receive [17]. Survivors are also at higher risk for developing other cancers, which may be the result of radiation treatment [16]. Today’s medulloblastoma research seeks to improve survival rates and improve quality of life for survivors.

Hope through research

The SickKids Brain Tumour Research Centre has a long history of groundbreaking medulloblastoma research. The 4 subgroups of medulloblastoma, today a fundamental consideration in both medulloblastoma research and treatment, were first described by BTRC researchers [4]. Today, the BTRC continues to investigate new ways to treat and prevent medulloblastoma. Every year, Meagan Bebenek Foundation provides seed grant funding for new research projects. Seed grants fulfill a specific, important need. When scientists apply for government funding and grants from large organizations, they must submit preliminary evidence that their idea works. Seed grants provide the resources they need to get new ideas off the ground.

Seed grant support years ago made these works possible: Dr. Vijay Ramaswamy’s lab at the BTRC recently published a study identifying a drug that works with radiation to treat one of the most high-risk subtypes of medulloblastoma. They received an MBF seed grant years prior, when the project began as an idea: could we make radiation treatment more effective, without increasing doses?

The drug they identified sensitizes medulloblastoma cells to radiation treatment in mice, meaning lower doses of radiation were effective in increasing survival. Lower doses would mean patients could experience fewer side effects and long-term negative impacts from radiation. This drug is undergoing early clinical trials in patients with other cancer types, and results suggest it’s safe, opening the possibility for trials in medulloblastoma patients in the future. A recently published medulloblastoma study from Dr. Peter Dirks’s lab at the BTRC also got its start as an MBF seed grant-funded idea: Can we prevent post-treatment medulloblastoma cells from reawakening and causing disease relapse? Death due to medulloblastoma is usually not from the original tumour, but from relapse or metastasis: when the tumour grows back after treatment.

Their study was based on knowledge that medulloblastoma tumours are not a single, homogeneous population of cells. Rather, they contain a multitude of cell types. They discovered the cell type that was responsible for reestablishing the cancer during relapse, and a drug that could target it.

Existing treatments can shrink or eliminate medulloblastoma tumours in mice, but the cancer often returns. When the Dirks Lab gave mice their drug after treatment, it prevented the tumours from growing back, showing that this treatment strategy could have the ability to prevent relapse, the leading cause of death from M

What’s on the horizon?

Recent MBF seed grants are helping BTRC researchers get new ideas off the ground. In 2024 Dr. Xi Huang’s lab received a grant to support their idea to unleash the immune system to fight medulloblastoma. Immunotherapy is treatment strategy that has been used successfully for other cancer types and involves using a patient’s own immune system to fight a tumour. Unfortunately, in medulloblastoma, the blood-brain-barrier is an obstacle that prevents most immune cells from reaching the cancer. The Huang lab has found a specific gene that regulates the blood-brain-barrier in medulloblastoma, and a seed grant will help them test whether targeting this gene with a drug could open the barrier and allow immune cells access to medulloblastoma tumours. Dr. Jane McGlade’s lab also received an MBF seed grant in 2024, which will allow them to investigate some of the inner workings of medulloblastoma cells. They are focusing in on a specific protein with a crucial role in brain development and how it may help medulloblastoma to grow when mutated. This grant will support a study revealing how normal and mutated versions of this protein interact with other proteins inside medulloblastoma cells. Understanding the underlying mechanisms behind cancer growth is important in finding new aspects of these tumours to target with treatments.

Too many children still do not survive medulloblastoma, and those that do are at risk of long-term health effects from current treatments. With the support of Meagan Bebenek Foundation, BTRC scientists are finding ways to make treatment more effective and more targeted, and to reduce both long- and short-term side effects, with the goal of improving survival and quality of life for children with medulloblastoma.

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