Brain tumors occur when cells in the brain grow uncontrollably, and are classified as either malignant (cancerous) or benign (non-cancerous), as well as primary (starting in the brain) or secondary (metastasized from elsewhere). Symptoms, which depend on the tumor's size and location, can include headaches, seizures, vision problems, and mental changes, though the cause of most cases is unknown; risk factors include CT scan radiation, vinyl chloride, and inherited syndromes like neurofibromatosis. Diagnosis is typically made via CT or MRI scans, often confirmed by a biopsy, and treatment may involve surgery, radiation, and chemotherapy, with outcomes varying widely—malignant glioblastomas have poor prognoses, while benign meningiomas usually fare well, and the average five-year survival rate for malignant brain cancers in the U.S. is 33%. Secondary (metastatic) brain tumors are about four times more common than primary ones, with roughly half originating from lung cancer, whereas primary tumors affect about 250,000 people globally each year, constituting less than 2% of all cancers and being the second most common cancer in children under 15. The economic burden is significant, as a 2005 case in New South Wales, Australia, had an average lifetime cost of AU$1.9 million, the highest of any cancer type, and while benign tumors only grow locally, they can still be life-threatening depending on size and location. Ongoing research is exploring immune-based treatments, and although most brain tumor causes remain unknown, studies on mobile phone exposure have not shown a clear risk.