A brain tumor is a mass of abnormal cells in the brain. If you think about it in its most basic form, the brain is an elaborate, elegant and sophisticated mass of tissue and nerve cells. It seamlessly controls our personality, our senses, helps regulate vital body functions and controls how we move in our environment. When abnormal cells grow in the brain to develop a tumor, it can disrupt how we function and requires treatment considerations that balance how the tumor is treated with how well the brain operates.