The International RadioSurgery Association says that brain cancer makes up 2 percent of cancers in the United States. One type of brain cancer is glioblastoma multiforme, a grade IV astroyctoma. Glioblastoma multiforme accounts for 50 percent of gliomas, according to the University of Connecticut. As a grade IV brain tumor, glioblastoma multiforme are the most malignant type of astrocytoma. This type of brain tumor starts from astrocytes, a type of glial cell, which are supportive cells in the brain. While gliomas can occur without a known cause, certain conditions play a role in the onset of glioblastoma multiforme.

Exposure

Some glioblastoma multiforme patients develop the brain tumor after exposure to certain substances. For example, the Children's Hospital Boston says that some patients develop the brain tumor after exposure to vinyl chloride. Manufacturers use vinyl chloride to produce polyvinyl chloride, or PVC. The Agency for Toxic Substances and Disease Registry describes vinyl chloride as having a sweet smell. People exposed to high doses of ionizing radiation directed at the brain, the type of radiation used in radiation therapy, may develop a glioblastoma multiforme.

Chromosomal Differences

Glioblastoma multiforme can result from changes in chromosomes. Humans have 23 pairs of chromosomes, which contain DNA. Alterations in the number of chromosomes or to the actual chromosome can result in problems. For example, the University of Connecticut says that patients with glioblastoma multiforme can have an altered or missing chromosome 17. As a result, patients have an inactive p53, a tumor suppressor gene, which is located on chromosome 17. The International RadioSurgery Association adds that 80 percent of glioblastoma multiforme patients have additional copies of chromosome seven. Other chromosomes may be linked to the formation of glioblastoma multiforme. The Atlas of Genetics and Cytogenetics in Oncology and Haematology lists changes to chromosomes four, nine, 10, 13, 19 and 22 as other chromosomal differences that may cause a glioblastoma multiforme brain tumor.

Hereditary Conditions

The Children's Hospital Boston says that people with certain conditions that run in the family have a higher occurrence of glioblastoma multiforme brain tumors, suggesting a hereditary link. For example, glioblastoma multiforme brain tumors occur more frequently in families that have a history of hereditary nonpolyposis colon cancer. Glioblastoma multiforme brain tumors are also more common among families with tuberous sclerosis, Turcot's syndrome, neurofibromatosis and Li-Fraumeni syndrome. GeneReviews says that Li-Fraumeni syndrome predisposes patients to brain tumors and other cancers, including soft-tissue sarcoma and adrenocortical carcinoma.