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Radiation

Following surgery, medulloblastoma is usually treated with radiation therapy. It is an important “next-step” because microscopic tumor cells can remain in the surrounding brain tissue even after surgery has successfully removed the entire visible tumor. Since these remaining cells can lead to tumor regrowth, the goal of radiation therapy is to reduce the number of left-over cells. Doctors consider several factors in planning radiation therapy: The age of the patient, the location of the tumor, the amount of remaining tumor, and any tumor spread. Since radiating the brain and central nervous system can be damaging to a developing brain, it is usually delayed in children under age 3. Initial treatment for these young children includes surgery followed by chemotherapy to control the tumor. Radiation may be delivered later, if needed.

For older children and adults, conventional external beam radiation therapy is given to the brain and spine. This area is called the craniospinal axis. This form of radiation is given 5 days a week for 5 to 6 weeks. A “boost” is given to the posterior fossa, the region most at-risk because it housed the original tumor. An additional boost may be given to areas of tumor spread. Age and risk factors determine the total doses of radiation given to each area.

While radiation therapy has proven effective, scientists are still looking for new ways to lower the potential side effects of this treatment. Techniques such as focused radiation, also called stereotactic radiosurgery, aims converged beams of radiation at the tumor. Conformal radiation allows doctors to shape the radiation beams to match the tumor’s contour. The goal of these focused forms of radiation is to spare normal brain tissue while treating tumor. Your radiation oncologist, a doctor specially trained in the use of radiation therapy, can talk with you about the best method of radiating you/your child’s tumor.

Treatment

If the tumor is determined to be a medulloblastoma, current treatment consists of surgically removing as much tumor as possible, followed by craniospinal (brain and spine) radiation and/or chemotherapy. Your doctor will suggest a treatment plan based on factors that indicate the risk of tumor recurrence — either “average-risk”

or “high-risk.” To determine risk, doctors look at the age of the patient; the amount of tumor remaining following surgery; and the amount of metastases, or tumor spread (also called M stage). Children are considered at “average-risk” of recurrence if they are diagnosed after age 3; if all, or nearly all, of the tumor is surgically removed; and if there is no evidence of metastases or tumor spread. All other pediatric medulloblastomas are considered to be at “high-risk” of recurrence. High-risk patients include those under age 3; if more than 1.5 cm (about 1/2 inch) of tumor volume remains following surgery; or if there is any evidence that the disease has spread. For adults, risk is generally determined by the amount of remaining tumor, and the presence or absence of tumor spread. The present staging system for medulloblastoma is of major importance. However, a variety of molecular changes were recently identified in childhood medulloblastoma tumors. Researchers are studying whether these findings will be helpful in determining whether children are of average or high-risk disease, or if the information might help to predict the chances of recurrence or spread. Researchers are also studying ways to obtain this biologic information in real-time (meaning within days after surgery).

M STAGE

“M stage” is a medical way of indicating the degree of metastasis (tumor spread), if any.

M0 means no evidence of metastasis has been found — the tumor appears to be limited to the area in which it grew.

M1 means there are tumor cells in the spinal fluid.

M2 means the tumor has spread within the brain.

M3 means the tumor has spread into the spine.

M4 means tumor spread away from the brain or spine (for example, in the rare situation in which the medulloblastoma spread to the chest or bones).

Surgery

Removing as much tumor as possible is the most important step in treating medulloblastoma. The neurosurgeon has three goals for the surgery:

-         To relieve cerebrospinal fluid buildup caused by tumor or swelling;

-         To confirm the diagnosis by obtaining a tissue sample; and

-         To remove as much tumor as possible with minimal neurological damage.

Several studies have shown the best chance for long-term tumor control is when all of the medulloblastoma visible to the neurosurgeon’s eye can be removed safely. Many technologically-advanced surgical tools are now available. MRI scanning combined with computer-aided navigation tools help the neurosurgeon map the exact tumor location before the operation, and track its removal during the procedure. High-powered microscopes provide visual enhancement. Ultrasound and gentle suction devices are used to remove tumor during the actual procedure. These techniques assist the surgeon in navigating around adjacent healthy structures.

While the goal is to eliminate the tumor, some medulloblastomas cannot be removed completely. In one-third of patients, the tumor grows into the brain stem, making total removal difficult because of potential neurological damage. If the tumor is determined to be inoperable, a biopsy may still be done to confirm the diagnosis. Steroids are drugs used before and after surgery to reduce swelling around the tumor.Occasionally, a ventriculostomy (an external drainage device) may be placed to divert excess cerebrospinal fluid from the brain. A permanent shunt, a long catheter-like tube that drains fluid from the brain to the abdomen, is sometimes necessary. In most cases, however, removing the tumor opens the cerebrospinal pathways, which restores both normal fluid flow and pressure. It also eliminates the need for a shunt or drainage device. Within two days following surgery, an MRI will be done to visualize the amount of remaining tumor. (If an MRI scanner is available in the operating room, the scan may be done during surgery.) The amount of “residual” or remaining tumor will be a strong factor in determining further treatment.

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Diagnosis

Obtaining a symptom history and performing a neurological examination will be your doctor’s first steps in making a diagnosis. Magnetic resonance imaging (MRI), done both with and without a contrast dye, is then used to identify the presence of a tumor in the brain. The contrast dye is given intravenously (into the vein) to enhance the pictures. By concentrating in abnormal tissue, the dye makes a tumor appear much brighter than other areas. If a tumor suspected of being a medulloblastoma is identified, an MRI of the entire spine can be done to look for tumor in that area. PET (positron emission tomography) and MRS (magnetic resonance spectroscopy) may be used to determine if what is seen on the scan is growing, live tumor as opposed to radiation effects or non growing tissue.

While scans provide important and intricate details, microscopic examination of tissue obtained during a surgical procedure, such as a biopsy or tumor removal, confirms the diagnosis. The pathologist, a doctor who specializes in studying tissue samples, will be looking for cell patterns that identify the tumor type. A pathology report usually takes about a week to be completed. It is sent to your neurosurgeon’s office, and the results then shared with you.

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Symptoms

The early “flu-like” signs of this tumor — lethargy, irritability and loss of appetite — are often so nonspecific that the disease first goes unnoticed. In infants, increased head size and irritability may be the first symptoms. Older children and adults may

experience headaches and vomiting upon awakening. Typically, the person feels better after vomiting and as the day goes on. As the pressure in the brain increases due to a growing tumor or blocked fluid passages, the headaches, vomiting and drowsiness may increase. Other symptoms depend on the nerves and brain structures affected by the tumor. Since medulloblastomas appear in the cerebellum, the center of balance and movement, problems with dizziness and coordination are common. Tumors growing close to the brain’s fourth ventricle may expand into that cavity, blocking the normal flow of cerebrospinal fluid. This can result in hydrocephalus — the buildup of cerebrospinal fluid within one of the cavities of the brain. The pressure of this buildup triggers the tumor’s characteristic symptoms: Morning headaches, nausea, vomiting and lethargy.

Children with this tumor may exhibit a clumsy, staggered walking pattern. They may also complain of visual problems. For instance, if the tumor involves the sixth cranial nerve which controls outward muscle movement of the eye, diplopia (double vision) can occur. Nystagmus (involuntary jerking of the eye) may also be a problem. While seizures are not common with medulloblastoma, other symptoms such as mild neck stiffness and a tilt of the head may occur. As many as 2 out of every 10 children with medulloblastomas may be less than 2 years of age at the time of diagnosis. In infants, symptoms can be more subtle and include intermittent vomiting, failure to thrive, weight loss, an enlarging head with or without a bulging of the soft spot of the head (fontanelle), and inability to raise the eyes upward (the so-called “sun-setting” sign).

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Incidence

About 1,000 new patients — children and adults — are diagnosed in the US each year, more often in males than females. Medulloblastoma is relatively rare, accounting for less than 2% of all primary brain tumors (tumors that begin in the brain or its coverings) and 18% of all pediatric brain tumors. More than 70% of all pediatric medulloblastomas are diagnosed in children under age 10. Very few occur in infancy or under age 1. Typically a tumor of childhood, medulloblastoma in adults is not common, but does occur. About one-third of all medulloblastomas diagnosed in

the United States are found in adults between the ages of 20 – 44. The incidence in adults sharply decreases in frequency after age 45, with very few older adults having this tumor.

Cause

Although the cause of medulloblastoma is unknown, scientists are making significant progress in understanding its biology. Changes have been identified in genes and chromosomes (the cell’s DNA blueprints) that may play a role in the development of this tumor. For example, one-third to one-half of all pediatric medulloblastomas contain a change on chromosome 17. Similar changes on chromosomes 1, 7, 8, 9, 10q, 11 and 16 may also play a part.

There are a few rare, genetic health syndromes that are associated with increased risk for developing this tumor. For instance, a small number of people with Gorlin’s Syndrome develop medulloblastoma. (Gorlin’s Syndrome is an inherited tendency to develop basal cell carcinoma in combination with other conditions.) Scientists have identified alterations on a gene called PTCH which may be the common link.

Similarly, genetic changes in the APC and TP53 genes are involved in two other inherited syndromes, Turcot and Li-Fraumeni. People with these syndromes tend to develop multiple colon polyps and malignant brain tumors.

Researchers are also exploring normal brain activity pathways, such as communication patterns among cells or genes. Changes in the genes involved in cell-signaling pathways such as SHH, WNT and ERBB, have been linked to the development of medulloblastoma. Several therapies targeted at proteins in these pathways are being studied.With increased understanding of how these genetic changes contribute to medulloblastoma, researchers may one day be able to correct or compensate for these changes.

Genetic versus Inherited

“Genetic” does not mean “inherited.” Genetic changes are those that occur in the DNA, or the inside blueprint, of a cell. No one knows what triggers these changes. Some, but not all, genetic changes can be inherited. Inherited means abnormal genes are passed from one generation to another. Medulloblastoma is not an “inherited” disease.