What is a Midline Glioma?
A midline glioma is an aggressive cancerous tumor that develops in the central structures of the brain and spinal cord. These tumors most commonly occur in the thalamus, brainstem (including the pons, medulla, and midbrain), and sometimes the spinal cord. Because these areas are located deep within the brain and control many essential functions, midline gliomas can be particularly difficult to treat.
Midline gliomas can occur at any age but are most commonly diagnosed in children, adolescents, and young adults. A subtype known as diffuse intrinsic pontine glioma (DIPG) is now classified within the broader category of diffuse midline gliomas.
Why are Midline Gliomas Challenging?
The location of a midline glioma is one of the primary reasons it is so difficult to treat. The brain’s central structures serve as critical communication pathways, relaying signals that control movement, sensation, speech, swallowing, balance, vision, and other vital functions.
Because these tumors grow within highly specialized and essential areas of the brain, even small changes can cause significant symptoms. Additionally, the tumor cells often infiltrate healthy brain tissue, making surgical removal extremely difficult and, in many cases, impossible.
Symptoms of a Midline Glioma
Symptoms vary depending on the tumor’s exact location and size but may include:
- Double vision or vision changes
- Slurred speech
- Difficulty swallowing
- Weakness or paralysis
- Balance and coordination problems
- Changes in sensation
- Headaches
- Fatigue
- Seizures (less common, depending on tumor location)
Because these tumors affect areas responsible for many critical functions, symptoms can sometimes progress rapidly. Symptom management may look different for each case.
How is a Midline Glioma Diagnosed?
Magnetic resonance imaging (MRI) with and without contrast is the gold standard for diagnosing and monitoring midline gliomas.
In many cases, physicians will perform a biopsy to obtain a small tissue sample. This tissue is used to confirm the diagnosis and perform molecular testing, which helps identify genetic alterations that may guide treatment decisions.
The H3K27 Mutation
Many diffuse midline gliomas contain a genetic alteration known as the H3K27 mutation. This mutation affects histone genes, which help regulate how DNA is packaged and used within cells.
When this process is disrupted, cells can lose normal growth control and begin dividing uncontrollably. The H3K27 alteration is considered a key driver of tumor growth and is a defining feature of many diffuse midline gliomas.
Identifying this mutation through molecular testing is important because it can help confirm the diagnosis and may provide opportunities for targeted treatment approaches.
The Importance of Molecular Testing
Comprehensive molecular testing has become an essential part of brain tumor care. By analyzing the genetic and molecular characteristics of a tumor, physicians can:
- Confirm the diagnosis
- Identify important mutations
- Determine eligibility for clinical trials
- Explore targeted treatment options
- Contribute to future treatment discoveries
Even when a specific mutation cannot immediately be targeted with a therapy, the information gained through molecular testing may become valuable as new treatments are developed.
Treatment Options for Midline Glioma
Surgery
Unlike many other brain tumors, midline gliomas are rarely removable through surgery. These tumors often grow between and around healthy brain cells within critical structures such as the brainstem and thalamus.
When possible, a biopsy is performed to obtain tissue for diagnosis and molecular testing. In select cases, surgeons may remove a small portion of the tumor if it extends into a more accessible area, but complete removal is generally not possible.
Radiation Therapy
Radiation therapy remains the standard treatment for most midline gliomas. Treatment is typically delivered five days per week over five to six weeks.
Radiation can help:
- Slow tumor growth
- Reduce symptoms
- Preserve neurological function
- Improve quality of life
Chemotherapy
Chemotherapy may be used alongside radiation therapy. Temozolomide is one of the most commonly used medications and may help slow tumor progression in some patients.
Steroids
Steroids do not treat the tumor itself but can reduce inflammation and swelling around the tumor. This may help relieve symptoms and improve neurological function.
Emerging Therapies and Clinical Trials
Research into midline glioma treatments is advancing rapidly.
One promising therapy is dordaviprone, commonly known as ONC201, a medication that received FDA accelerated approval for certain patients with recurrent H3K27-mutant diffuse glioma following radiation therapy. Early studies have demonstrated encouraging responses in some patients.
Researchers are also investigating:
- ONC206, a next-generation version of ONC201
- Immunotherapy approaches
- Checkpoint inhibitors
- Cancer vaccines
- Monoclonal antibodies
- CAR T-cell therapy
CAR T-cell therapy uses a patient’s own immune cells, which are modified in a laboratory to better recognize and attack cancer cells. While still being studied, this approach represents a promising avenue for future treatment.
Looking Ahead
While diffuse midline gliomas remain among the most challenging brain tumors to treat, advances in molecular testing, targeted therapies, immunotherapy, and clinical trial research are creating new opportunities for patients and families.
Researchers continue to learn more about the genetic drivers behind these tumors, leading to more precise treatment strategies and renewed hope for improved outcomes in the future.
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The above information is from the World Health Organization (WHO) Central Nervous System (CNS) Tumors Classification of Tumours and the Central Brain Tumor Registry of the United States (CBTRUS) unless otherwise noted. It was written by Head for the Cure staff and medically reviewed by members of the Medical Advisory Board.