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Medulloblastoma is the most common malignant brain tumor in children. Medulloblastoma begins in the cerebellum, an area in the back of the brain.
There are about 500 new cases of pediatric medulloblastoma every year in the United States. They account for 20% of childhood central nervous system (CNS) tumors. Medulloblastoma is most common in children under 16 years of age. It is most often diagnosed between 5 and 9 years of age. However, medulloblastoma may be seen in older teens and, less commonly, in adults.
Medulloblastoma can be divided into four subgroups based on molecular features of tumor cells:
The specific subgroup influences medulloblastoma 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.
Medulloblastomas are fast growing, and these tumors often spread to other parts of the brain and spinal cord. The overall survival rate for childhood medulloblastoma is 70-80% if the disease has not spread. If the disease has spread, the survival rate is about 60%. However, the specific type of medulloblastoma, including molecular subgroup, can influence treatment and prognosis.
Signs and symptoms of 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 the tumor has spread to the spinal cord, symptoms may include:
Symptoms of medulloblastoma depend on tumor size and location. Medulloblastoma is a cerebellar tumor. 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.
Most medulloblastomas develop in the middle of the cerebellum by the fourth ventricle. As the tumor grows, it can block the normal flow of cerebrospinal fluid. This causes a buildup of fluid within the brain known as hydrocephalus. The fluid increases pressure on the brain (intracranial pressure). Many of the symptoms of medulloblastoma are due to hydrocephalus.
Certain gene and chromosome changes 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.
Doctors evaluate medulloblastoma in several ways.
Medulloblastoma can be classified or described based on certain features such as histology, molecular features, and metastasis. Tissue histology, molecular features of the tumor cells, and stage are used to categorize patients with medulloblastoma based on disease risk and prognosis. This helps doctors match treatment plans to medulloblastoma risk group.
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 tested to learn about the genetic and molecular features of the tumor cells. Based on the molecular profile, medulloblastomas are grouped as WNT, SHH, Group 3, or Group 4.
Where the medulloblastoma tumor is located within the cerebellum can also provide a clue as to the molecular type of medulloblastoma. WNT medulloblastoma tumors tend to occur along the midline of the cerebellum. SHH medulloblastoma tumors tend to be found in the lateral part of the cerebellum.
Medulloblastoma may also be classified by metastasis, or spread of disease:
The overall five-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 cure include:
|WNT subtype||SHH subtype||Group 3||Group 4|
|% of Cases||10% of medulloblastomas||30% of medulloblastomas||25% of medulloblastomas||35% of medulloblastomas|
|Patient Characteristics||Most common in older children and teens; rare in infants||Most common in young children under 3 years of age and in older teens and adults||Most common in Infants and young children; rare in teens; more common in males||Found in all age groups but rare in infants; more common in males|
|Medulloblastoma Histology||• Classic (most often)
• Large Cell Anaplastic (rare)
|• Desmoplastic / nodular
• Large Cell Anaplastic
• Large Cell Anaplastic
• Large Cell Anaplastic (rare)
|Metastasis at Diagnosis||5-10% of patients have metastatic disease at diagnosis||15-20% of patients have metastatic disease at diagnosis||30-45% of patients have metastatic disease at diagnosis||35-40% of patients have metastatic disease at diagnosis|
|Recurrence||Rarely recurs||If it recurs, it is usually local disease||If it recurs, it is usually metastatic||If it recurs, it is usually metastatic|
|5-year Survival Rates for Medulloblastoma||>90% survival||75% survival||50% survival||75% survival|
|Overall Medulloblastoma Prognosis||Very good||Intermediate, but infants have a better prognosis||Poor||Intermediate|
Medulloblastoma treatment includes surgery, radiation to the brain and spine (except in children under 3 years of age), and chemotherapy.
Current risk-based approaches to medulloblastoma treatment classify patients based on tumor 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. In many cases of medulloblastoma, most or all of the tumor can be removed with surgery. However, in some cases, the location of the tumor may limit how much can be removed safely.
Posterior fossa syndrome, or cerebellar mutism, is a rare condition that sometimes develops after surgery to remove a brain tumor in the posterior fossa region of the brain. About 25% of children who have surgery for medulloblastoma will develop posterior fossa syndrome. Symptoms include changes in speech, swallowing, movement, emotions, and behavior. The syndrome develops 1-10 days after tumor surgery, and symptoms can last weeks, months, or longer. Symptoms can be mild or severe, and most children improve over time. The condition is not fully understood, and doctors do not know why it affects some children and not others. Care for posterior fossa syndrome usually includes a combination of rehabilitation services including physical therapy, occupational therapy, and speech therapy.
Radiation therapy is usually used after surgery for medulloblastoma. The dose of radiation therapy depends on the stage of disease and patient risk category. In general, radiation is delivered to the brain and spine (craniospinal irradiation) with a higher dose (boost) at the primary tumor site. Because of the potential health risks, radiation therapy is not used in very young children.
Doctors may use newer types of radiation therapy such as proton beam radiation to treat medulloblastoma. In this type of radiation therapy, the amount of energy and how deep it goes into the tumor can be tailored to match the tumor size and shape. This allows doctors to aim high doses of radiation at the tumor, reducing damage to nearby healthy cells. However, 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 type of 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 the prognosis is usually poor. Young children with high-risk medulloblastoma may experience side effects of treatment that outweigh the possible benefits of treatment.
Increased understanding of medulloblastoma has led to improved treatments and better survival rates in recent years. However, medulloblastoma survivors often suffer a variety of treatment-related problems. Ongoing follow-up care, laboratory tests, and routine MRI scans are used to monitor patients after completion of treatment. Monitoring should focus on early detection of recurrence and long-term and late effects of treatment. Care should also include appropriate rehabilitation and neurological consultation.
Medulloblastoma survivors have an increased risk of certain late effects based on the treatments they received including chemotherapy and radiation therapy. These problems may include:
Children treated for medulloblastoma may have future problems in areas of daily life such as school, work, and relationships. They may also have lower physical fitness and physical function. Regular checkups and screenings by a primary care physician are important to watch for health problems that can develop years after therapy. An interdisciplinary care team can provide a personalized care plan to promote long-term health and quality of life. Support services such as mental health and academic resources can also promote quality of life for survivors.
Reviewed: February 2020