Glioblastoma, also known as glioblastoma multiforme (GBM), is the most aggressive type of cancer that begins within the brain. Initially, signs and symptoms of glioblastoma are nonspecific. They may include headaches, personality changes, nausea and symptoms similar to those of a stroke. Symptoms often worsen rapidly and may progress to unconsciousness.The cause of most cases of glioblastoma is not known. Uncommon risk factors include genetic disorders, such as neurofibromatosis and Li–Fraumeni syndrome, and previous radiation therapy. Glioblastomas represent 15% of all brain tumors. They can either start from normal brain cells or develop from an existing low-grade astrocytoma. The diagnosis typically is made by a combination of a CT scan, MRI scan and tissue biopsy.There is no known method of preventing the cancer. Treatment usually involves surgery, after which chemotherapy and radiation therapy are used. The medication temozolomide is frequently used as part of chemotherapy. High-dose steroids may be used to help reduce swelling and decrease symptoms. Greater surgical removal of the tumor is linked to longer survival.Despite maximum treatment, the cancer usually recurs. The typical duration of survival following diagnosis is 12 to 15 months, with fewer than 3 to 7% of people surviving longer than five years. Without treatment, survival is typically three months. It is the most common cancer that begins within the brain and the second-most common brain tumor, after meningioma. About 3 in 100,000 people develop the disease per year. It most often begins around 64 years of age and occurs more commonly in males than females. Immunotherapy is being studied as treatment for the cancer.