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Medulloblastoma is a cancerous tumor of the brain. It is the most common malignant brain tumor in children, accounting for 20% of childhood central nervous system (CNS) tumors. There are between 250 and 500 new cases of pediatric medulloblastoma every year in the United States.
These tumors are most common in children under 16 years of age and are most often diagnosed between 5 and 9 years of age. However, medulloblastomas may be seen in older teens and, less commonly, in adults.
Medulloblastoma begins in the cerebellum, an area in the back of the brain. Specifically, the cerebellum is found in the lower rear part of the brain, in a region known as the posterior fossa. Functions of the cerebellum include the control of movement, balance, posture, and coordination.
Medulloblastomas are fast growing, and these tumors often spread to other parts of the brain and spinal cord. Most medulloblastomas are located in the middle of the cerebellum by the fourth ventricle.
Medulloblastoma can be divided into four subgroups based on molecular features of tumor cells:
The specific medulloblastoma subgroup influences prognosis. Doctors use subgroups to classify patients into risk categories. This information helps doctors plan appropriate treatments.
Treatment for medulloblastoma includes surgery to remove as much of the tumor as possible. Radiation therapy is used after surgery to kill any remaining cancer cells. Chemotherapy is also used together with surgery and radiation therapy.
The overall survival rate for childhood medulloblastoma is 70-80% if the disease has not spread. If the disease has spread, the average survival rate is about 60%. However, the specific type of medulloblastoma tumor, including molecular subgroup, can influence treatment and prognosis.
Certain changes in genes and chromosomes within the tumor cell are associated with the development of medulloblastoma. Usually, it is not known why these genetic changes occur.
Most medulloblastomas occur in children between ages 5 and 9 years old. It is rare in infants and adults. Medulloblastoma is slightly more common in boys than in girls.
Some children may be at increased risk for brain tumors due to rare inherited conditions. These syndromes include Gorlin’s syndrome, Turcot syndrome, and Li-Fraumeni syndrome.
Symptoms of childhood medulloblastoma depend on several factors including the size and location of the tumor and the child’s age and stage of development.
Medulloblastoma symptoms include:
If there is spread of tumor to the spinal cord, symptoms may include:
As the tumor grows, it often blocks the normal flow of cerebrospinal fluid. This causes a buildup of fluid within the brain known as hyrodcephalus. The fluid increases pressure on the brain (intracranial pressure). Many of the symptoms of medulloblastoma are due to the increased pressure against brain tissue.
Doctors evaluate medulloblastoma in several ways.
Microscopic features of the tumor cells such as the size and shape are used to classify medulloblastoma tumors by histology:
Anaplastic and large cells often occur together and are grouped as large/cell anaplastic (LCA) tumors.
Tissue from the tumor is also analyzed for biomarkers that give information on the genetic and molecular features of the tumor cells. Based on the molecular profile, medulloblastomas are grouped as WNT subgroup, SHH subgroup, Group 3, or Group 4.
Tumor location within the cerebellum can provide a clue as to the molecular type of medulloblastoma. WNT tumors tend to occur along the midline of the cerebellum. SHH tumors tend to be found in the lateral part of the cerebellum.
Tissue histology and molecular features of the tumor cells are used to categorize patients with medulloblastoma and predict outcomes. This helps doctors more specifically match treatment plans to medulloblastoma risk group.
Medulloblastoma may also be classified by metastasis:
The overall 5-year survival rate for pediatric medulloblastoma is approximately 70-80% if the disease has not spread. For high risk patients, the survival rate is about 60-65%.
Factors that affect chance of recovery include:
||General Patient Characteristics
||Metastasis at Diagnosis
~10% of medullobastomas
|Most common in older children and teens; rare in infants
Very rare Large Cell Anaplastic
~30% of medulloblastomas
|Most common in young children under 3 years of age and older adolescents/adults
Large Cell Anaplastic
||Intermediate, but infants have a better prognosis
~25% of medulloblastomas
|Most common in Infants and young children; rare in teens; more common in males
||Classic and Large Cell Anaplastic
~35% of medulloblastomas
|Found in all age groups but rare in infants; more common in males
||Classic; rarely Large Cell Anaplastic
Treatment for medulloblastoma includes surgery, radiation to the brain and spine (except in infants and young children), and chemotherapy.
Current risk-based approaches to medulloblastoma treatment classify patients based on clinical and molecular features and predicted outcomes. Doctors consider:
The goal of a risk-based approach is to achieve survival while lowering the risk of side effects due to treatments. For patients who are predicted to have good outcomes, lower intensity therapy can reduce long-term problems from radiation and chemotherapy. For high-risk patients, more intensive therapy can improve chance of survival.
Patients may be offered treatment within a clinical trial.
Surgery to remove as much of the tumor as possible is a main treatment for medulloblastoma. The goal is gross total resection, or complete removal of the tumor. However, location of the tumor may limit how much can be removed.
Radiation therapy is usually used after surgery for medulloblastoma. The dose of radiation therapy depends on the stage of disease. Because of the potential for late effects due to treatment, radiation therapy is not used in very young children.
Proton beam radiation therapy – In this type of radiation therapy, the amount of energy and how deep it goes into the tumor can be tailored to match each tumor’s size and shape. The radiation can stop at the tumor site. That means it doesn’t affect healthy tissue and organs on the other side of the tumor. This allows doctors to aim high doses of radiation at tumors and minimize damage to nearby healthy cells. Not every center offers proton therapy.
Chemotherapy is usually used along with radiation therapy and surgery to treat medulloblastoma. In very young children, chemotherapy may be used to help delay radiation until the child is older. High-dose chemotherapy with stem cell rescue may also be used.
The SHH subgroup is the most common medulloblastoma in children under 3 years of age followed by Group 3 tumors. SHH tumors in infants tend to have a favorable histology and molecular profile. These children often do well with surgery followed by chemotherapy without radiation.
Non-SHH medulloblastoma in infants is harder to treat, especially if there is metastatic disease. Treatments such as focal radiation therapy and high-dose chemotherapy with stem cell rescue may be tried, but cure is difficult to achieve. Side effects may outweigh the possible benefits in some cases.
Increased understanding of the molecular basis of medulloblastoma has led to improved rates of survival in recent years. However, survivors of medulloblastoma often suffer a variety of treatment-related complications. Ongoing follow-up care is needed to monitor patients for recurrence of disease and address long-term and late effects of treatment. Care should also include appropriate rehabilitation and neurological consultation.
About 25% of children who have surgery for medulloblastoma will develop posterior fossa syndrome. This syndrome usually develops within a few days after surgery. Symptoms include changes in speech, swallowing, motor function, and emotions. Symptoms can be mild or severe, and most children improve over time. The cause of posterior fossa syndrome is not known, and it is not possible to predict which patients will be affected.
Medulloblastoma survivors have an increased risk of specific late effects related to treatment. These include problems with endocrine function, cognition, hearing, fertility, and heart and lung function as well as increased risk of second cancers. Children treated for medulloblastoma often have difficulties in school, work, and relationships. They may have lower physical fitness and physical function. Regular physical checkups and screenings by a primary care physician are important to watch for health problems that can develop years after therapy. Support services such as mental health and academic resources can also promote quality of life for survivors.
Reviewed: June 2018