Childhood Brain Tumors: Facts and Figures

National Cancer Institute
Monday, 5 April 1999

Kinds of Brain Tumors

Cancer can spread, or metastasize, to the brain from other parts of the body or it can originate in the brain as a primary brain tumor. This fact sheet concerns only primary brain tumors.

Brain tumors account for about 90 percent of all primary central nervous system (CNS) malignancies in children and adolescents. (Other CNS cancers occur outside the brain, originating, for example, in the cranial nerves; the meninges, or membranes, surrounding the brain; and the spinal cord.)

There are different kinds of brain tumors and various systems for grouping them, according to the kind of cells in which the tumors develop and/or the part of the brain in which they originate. Most brain cancers develop from glial cells, which form supporting structures for nerve cells. Tumors originating in nerve cells are more rare.

The brain cancers most common in children and adolescents (ages 0-19 years) fall into three main groups:

- Astrocytomas, which arise from one kind of glial cells called astrocytes. Astrocytomas may grow anywhere in the brain or spinal cord, but in children, they occur in the brain stem, the cerebrum, and the cerebellum. A grade III* astrocytoma is sometimes called anaplastic astrocytoma. A grade IV astrocytoma is usually called glioblastoma multiforme. Also included in this category are brain stem gliomas, which occur in the lowest, stemlike part of the brain. Astrocytomas account for nearly 68 percent of CNS malignancies in children.

- Primitive neuroectodermal tumors (PNET), which are thought to develop from primitive (developing) nerve cells that normally do not remain in the body after birth. PNETs include medulloblastomas. These tumors account for about 21 percent of childhood CNS cancers.

- Ependymomas, which usually develop in the cells lining the ventricles (the four connected cavities in the brain). These tumors account for about 9 percent of CNS tumors in children.

Statistics

Childhood cancers of the brain and nervous system, while rare, are now the second leading cause of cancer-related deaths among children under age 20 in the United States, ranking only behind the leukemias. Cancer is the second leading cause of all deaths in children, after unintentional injuries.

About 2,200 new central nervous system cancers are diagnosed in the United States each year in children and adolescents under 20 years of age. The incidence rate is 27.2 cases per million children.

The highest incidence of CNS cancer is among children age 7 and younger. Rates are slightly higher in boys than in girls, largely because boys are more likely to develop primitive neuroectodermal tumors and ependymomas.

Rates are higher in white children than in black children. This difference between the races is seen primarily among boys and young children.

The incidence of childhood brain tumors (ages 0-14 years) rose from 1973 through 1995 (from 2.3 to 3.1 per 100,000), with the greatest increase occurring from l983 through l986. A recent study suggests that this rise may not represent a true increase in the number of cases, but may be due to better diagnosis using magnetic resonance imaging (MRI). This technique, which produces images of the brain using a powerful magnet linked to a computer, came into widespread use in the mid-1980s.

Survival rates for children and adolescents (0-19 years) vary by the type of tumor, but overall, about 65 percent of children with central nervous system tumors survive at least five years from the time of diagnosis, based on data from 1985-94. That represents an improvement over the earlier five-year survival rate (1975-84) of 59 percent.

Five-year survival rates are highest for children and adolescents with astrocytomas (74 percent), followed by other gliomas (57 percent), ependymomas (56 percent), and PNET or medulloblastoma (55 percent). Older children are more likely to survive than younger children. Very young children, especially infants with ependymoma or PNET, are at particularly high risk of death.

Causes and Risk Factors

There is no specific risk factor known to explain a substantial proportion of brain tumor occurrence. The two known risk factors -- therapeutic or high environmental doses of ionizing radiation to the head and certain genetic conditions -- account for only a small percentage of cases.

Children once treated with ionizing radiation for tinea capitis (ringworm of the scalp) are now known to have had an increased risk of brain cancer. This practice has been abandoned. Currently, children at risk from radiation treatments are those given radiotherapy to the head for leukemia or a previous brain tumor.

The genetic conditions linked to a greatly increased risk of brain cancer include neurofibromatosis, tuberous sclerosis, nevoid basal cell syndrome, Turcot syndrome, and Li-Fraumeni syndrome.

A somewhat increased risk has been observed when a sibling or parent has had a brain tumor, but the association with family history is not strong or consistent.

There is some limited evidence that diet during pregnancy may either raise or lower risk, but it is not known what elements of diet may be involved. Frequent consumption of cured meat has been associated with a small increased risk in a few studies, but it is unclear whether cured meats or another dietary factor is responsible, or even whether there is a consistent association. There have been only a few studies and most aspects of diet have not yet been examined.

Researchers have been able to determine that a few suspected risk factors are not likely to be linked with an elevated risk of childhood brain tumors. Passive cigarette smoke exposure, electric blanket use, and ultrasound testing during pregnancy have been shown not to increase the risk of brain tumors.

Other hypothesized risk factors, for which the evidence is so far inconsistent or limited, include exposure to electromagnetic fields, products containing N-nitroso compounds, and pesticides; father's occupation; history of head injury; and family history of epilepsy, seizures, or mental retardation.

National Cancer Institute Clinical Research

National Cancer Institute (NCI) supported clinical trials evaluating new treatments for children with brain tumors are being conducted at the NCI campus in Bethesda, Md., and at medical centers around the country. Most large clinical trials are carried out through NCI-sponsored Clinical Trials Cooperative Groups, which are networks of institutions and physicians throughout the United States and Canada that conduct studies jointly. Two of NCI's Cooperative Groups -- the Children's Cancer Group and the Pediatric Oncology Group -- focus on childhood cancers, including brain tumors. These two groups plan to merge with two other NCI-sponsored childhood cancer groups to form one Cooperative Group for children's cancers.

Some of the new therapies now under investigation in advanced trials (phase II and III) include new drugs, such as temozolomide, phenylacetate, and RMP-7 (an agent designed to help other chemotherapy drugs cross the blood-brain barrier). High-dose chemotherapy with stem cell transplantation is also under study for some brain tumors.

Radiation therapy has increased survival rates in brain cancer but can result in cognitive impairment, arrested growth, and other late effects. Some trials now are looking at alternative strategies, such as lower doses of radiation, chemotherapy in place of radiotherapy, and more focused delivery of radiation using conformal techniques.

The newest investigational approaches, now approaching initial trials in humans, include novel chemotherapy drugs; biological therapies; neurosurgical procedures; and radiotherapy techniques. NCI's new Pediatric Brain Tumor Consortium will conduct the initial trials of some of these innovative therapies, and those that appear promising will then be evaluated in larger, more definitive trials by the Cooperative Groups and others.

* In addition to cell of origin (histology) and location in which the tumor arises in the brain (anatomic site), brain tumors are categorized by how fast they grow and/or how severe the tumor is (grade). Slow-growing brain tumors are classified as Grade I or Grade II while faster growing tumors are classified as Grade III or Grade IV.

For more information, or to contact National Cancer Institute, see their website at: www.cancer.gov