Human: I have a friend who has just been diagnosed with a brain tumor. What is a brain tumor and what are the different types? Assistant: 
A brain tumor is a mass of abnormal cells that grows in the brain or spinal cord. There are many different types of brain tumors, including gliomas, meningiomas, pituitary adenomas, craniopharyngiomas, schwannomas, and other rare tumors. Brain tumors can cause symptoms like headaches, seizures, nausea, vomiting, vision changes, and difficulty speaking or thinking clearly.