Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) prostate cancer ?
    ### Response:
    Prostate cancer is a common disease that affects men, usually in middle age or later. In this disorder, certain cells in the prostate become abnormal and multiply without control or order to form a tumor. The prostate is a gland that surrounds the male urethra and helps produce semen, the fluid that carries sperm.
    