Brain Tumor: Medulloblastoma / PNET
Alternate Names: PNET
Medulloblastomas are tumors that arise in the posterior fossa region of the brain. The exact cell of origin is not known. These tumors are also referred to as primitive neuroectodermal tumor (PNET). Tumors that have the same characteristics can also arise in other parts of the brain. This tumor type has a tendency to spread to other areas of the brain and spinal cord.
- Medulloblastoma accounts for about 20 percent of childhood brain tumors.
- They most often occur in the first decade of life; half occur in children younger than five to six years of age.
- These tumors are slightly more common in males than in females.
Clinical Features and Symptoms
- Most patients have a history of headache and morning vomiting, which gets worse with time.
- Because of the tumor’s location, patients may also have clumsiness and problems with tasks like handwriting.
- Rarely patients can have visual loss at diagnosis.
- If the tumor has spread to the spinal cord, symptoms may include back pain, difficulty walking and inability to control bladder and bowel functions.
Survival ranges from 60 to 80 percent.
- Surgery, radiation therapy and chemotherapy are used to treat medulloblastoma. The aim of surgery is to remove as much tumor as possible. When surgery is done by highly skilled neurosurgeons using modern techniques, most tumors can be totally removed. After surgery, tests are performed to see if there is any residual tumor at the operated site and if and where the tumor has spread.
- Patients with totally resected tumors that have not spread are now treated with reduced-dose radiation to the brain and spinal cord. The goal is to decrease the long-term side effects of radiation. Then patients receive chemotherapy. In a national study, 80 percent of children treated in this way survived. More time is needed to see if this approach reduces late effects and improves quality of life.
- If the tumor has spread to other areas of the brain and spinal cord (or in rare cases, to the bone marrow) the patient is considered high-risk. These patients receive higher-dose radiation therapy before chemotherapy.
Current research on medulloblastomas is at several levels.
Basic (laboratory) scientists are trying to understand the genetic changes in the tumor cells that make them become cancerous. It is anticipated that some of the genetic characteristics will help identify which tumors require more or less aggressive therapy.
Radiation oncologists are studying giving radiation therapy to kill the tumor cells in ways that may reduce damage to nearby normal brain tissue.
Drug development studies have identified new agents that show promise in laboratory models of these tumors.
Another clinical approach is the use of blood stem cells to permit high-dose chemotherapy that would otherwise cause dangerously low blood counts.
Shorter, more intensive chemotherapy is currently being tested in children with both low-risk and high-risk tumors.
In our current research protocol, we are also studying ways by which we can reduce the loss of IQ following therapy for medulloblastoma/PNET.
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