Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Prostate Cancer ?
    ### Response:
    The prostate is a male sex gland, about the size of a large walnut. It is located below the bladder and in front of the rectum. The prostate's main function is to make fluid for semen, a white substance that carries sperm. Prostate cancer occurs when a tumor forms in the tissue of the prostate.
    