A brain tumor is an abnormal mass of cells in the brain that either begins in the brain (primary brain tumor) or grows from a cancer that begins elsewhere in the body and travels to the brain (metastatic, or secondary brain tumor). Brain tumors can be benign (not cancerous) or malignant (cancerous), and depending on the location, possible symptoms include unexplained nausea and vomiting, headaches that get progressively worse, seizures and personality changes.