The cause of most central nervous system tumors is not fully understood. But researchers have found some of the chemical changes that occur in normal brain cells that may lead them to form brain tumors.
Normal human cells grow and function based mainly on the information contained in each cell's chromosomes. Chromosomes are long molecules of DNA in each cell. Brain tumors, like other tumors, are caused by changes in a person's DNA. DNA is the chemical in each of our cells that makes up our genes — the instructions for how our cells function. We usually look like our parents because they are the source of our DNA. However, DNA affects more than how we look.
Some genes control when our cells grow, divide, and die. Certain genes that speed up cell division are called oncogenes. Others that slow down cell division, or cause cells to die at the right time, are called tumor suppressor genes. Cancers can be caused by DNA changes that turn on oncogenes or turn off tumor suppressor genes. These gene changes can be inherited from a parent or, more likely, may happen during a person's lifetime as cells in the body divide to form 2 new cells.
In recent years, researchers have found the gene changes that cause some rare inherited syndromes (like neurofibromatosis, tuberous sclerosis, Li-Fraumeni syndrome, and von Hippel-Lindau syndrome) and increase the risk of developing some central nervous system tumors. For example, the Li-Fraumeni syndrome is caused by changes in the p53 tumor suppressor gene. Normally, this gene prevents cells with damaged DNA from growing. Changes in this gene increase the risk of developing brain tumors (particularly gliomas), as well as some other cancers.
In most cases, it is not known why people without inherited syndromes develop changes in cells of their central nervous system. Most risk factors for cancer somehow damage genes. For example, cigarette smoke is a risk factor for lung cancer and several other cancers because it contains chemicals that can damage genes. The brain is relatively protected from cigarette smoke and other cancer-causing chemicals that we all breathe or eat, so these factors are not likely to play a major role in these cancers.
Normal cells usually require several different gene changes before they become cancerous. There are many kinds of brain tumors, each of which may have different sets of gene changes. A number of gene or chromosome changes have been found in different brain tumor types, but there are probably many others that have not yet been discovered.
Researchers now understand some of the gene changes that may occur in different types of brain tumors, but it's still not clear what might cause these changes. Some gene changes may be inherited, but most brain and spinal cord tumors are not the result of known inherited syndromes. Other gene changes may just be a random event that sometimes happens inside a cell, without having an external cause. Other than radiation, there are no known lifestyle-related or environmental causes of brain tumors, so it is important to remember that there is nothing these people could have done to prevent these cancers.
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