Changes in the genetic material may also occur because of exposure to infections, drugs, tobacco, chemicals or other factors. However, to date, the only known causes for brain tumors or cancers are: Previous radiation therapy to the head area. Exposure to some chemicals. These chemicals are: formaldehyde used by pathologists and embalmers, vinyl chloride used in the manufacturing of plastics and acrylonitrile used in the manufacturing of textile and plastics. Exposure to the textiles and plastics themselves does not increase the risk of developing brain cancer.