Brain tumors - primary
Description
An in-depth report on the causes, diagnosis, and treatment of brain tumors.
Alternative Names
Gliomas; Medulloblastoma
Risk Factors
Nearly 360,000 people in the U.S. are living with brain cancer. Men are at higher risk than women for most brain tumors. Primary malignant brain tumors are still uncommon and represent only 1.3% of all cancers diagnosed in the United States and 2.4% of all deaths due to cancer.
Primary brain cancers are rare, occurring in slightly more than 11 people per 100,000 per year. There has been some evidence of a growing incidence of brain cancer among the elderly since the 1980s. The increase, however, is most likely due to the rise in incidence of non-Hodgkin's lymphomas -- which can occur in the brain. When this malignancy is eliminated, any increase in other tumors is not significant.
Age
The average age of diagnosis for brain tumors is 57, and about 90% of primary brain tumors occur in adults. These tumors can develop at all ages, usually peaking in two age groups.
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In adults, ages 55 - 65
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In children, ages 3 - 12
Risk Factors in Children.
Tumors in the central nervous system are now the most common primary cancers in children, but they are still rare. An estimated 3,110 benign or malignant brain tumors are expected to be diagnosed in children each year. Brain tumors in children are more likely to occur in the cerebellum, the midbrain, or the optic nerve.
The incidence has increased over the past years, but there is some evidence that this increase is only due to better diagnostic procedures. The mortality rate has actually decreased. Researchers have attempted to uncover risk factors for childhood brain cancer. There may be some association between a higher risk and the following conditions:
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Children treated with radiation to the head for leukemia and who have a specific genetic defect may face a high risk for brain cancer. (It should be noted that for children without this defect, the risk is very small.)
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Having parents with specific cancers. (According to a 2000 study, having parents with nervous system cancers, colon cancer, or cancer in the salivary glands increased the risk of specific brain tumors in their children.)
Ethnicity
The risk for primary brain tumors in Caucasians is higher -- as much as twofold depending on type -- than in African-Americans.
Environmental or Occupational Risk Factors
Radiation Exposure.
People who receive radiation therapy to the head during cancer treatment have an increased risk of developing brain tumors 10 - 15 years later. Workers in the nuclear industry are also at increased risk.
There is no evidence that electromagnetic field exposure from power lines or household appliances poses any risk. Several recent epidemiological studies, including a 2006 study in the
British Medical Journal
, found that cell phones, cordless phones, and wireless devices are also safe and do not increase the risk for gliomas.
Chemical and Metals in Brain Tumors.
High exposure to numerous metals and chemicals have been associated with brain tumors:
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Industrial chemicals, including vinyl chloride and petroleum products
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Lead, arsenic, or mercury exposure
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Exposure to pesticides. A major study of pesticides is underway, but results are not in yet. A 2003 study indicated that parental exposure to pesticides or herbicides did not appear to be important in increasing risk for brain cancer in their children.
Brain cancer is uncommon, and, over the course of their lifetime, many people are exposed to these chemicals, many of which are very common. To date, there has been no clear evidence that implicates any specific industrial chemical or metal.
Inherited Disorders
About 5% of primary brain tumors are associated with hereditary disorders. They include:
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Li-Fraumeni cancer family syndrome
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Tuberous sclerosis
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Von Recklinghausen disease (neurofibromatosis)
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Von Hippel Lindau disease
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Familial polyposis (Turcot's syndrome)
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Osler-Weber-Rendu syndrome
Organ Transplantation
A 2002 study reported a higher risk for brain cancers in patients who had undergone organ transplantations. Researchers believed that the drugs used to suppress the immune response after the procedures may increase the risk.
Medical Conditions Associated with a Lower Risk for Brain Tumors
A 2002 study reported lower risks for brain cancers in individuals with allergies and autoimmune diseases (such as type 1 diabetes). Autoimmune diseases were also associated with a lower risk for meningiomas. The cause of this possible association remains unknown.
Studies have also found an association between lower risk for gliomas and a history of infection with varicella zoster, the virus that causes chicken pox and shingles.
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Review Date: 10/19/2006
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Reviewed By: Harvey Simon, M.D., Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital.
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