Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Oligoastrocytoma ?
    ### Response:
    Oligoastrocytoma is a brain tumor that forms when two types of cells in the brain, called oligodendrocytes and astrocytes, rapidly increase in number to form a mass.  These brain cells are known as glial cells, which normally protect and support nerve cells in the brain.
    