In the United States, between fifteen and twenty people out of every one hundred thousand develop brain cancer every year. When a brain tumor occurs, the ever-growing mass of cells compresses and damages other cells in the brain, interfering with brain function. The tumor pushes brain tissue around, creates pressure by pressing against the bones of the skull, and infiltrates healthy brain tissue and around nerves. Unlike other forms of cancer, which are associated with lifestyle activities such as smoking, dietary factors, or drinking, there is little known about why primary brain cancer occurs. Most brain cancer is the result of genetic mutations or changes in the genes that normally keep cells from reproducing in an uncontrolled manner. Because brain cancer is not associated with lifestyle or environmental factors that most people encounter, there is no known way to guard against it at this time, but genetic research and gene-based treatments offer great hope for a breakthrough and a possible cure of this dread disease.