Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Urachal cancer ?
    ### Response:
    Urachal cancer is a rare type of bladder cancer, making up less than 1% of all bladder cancers. Only about 350 cases have been described in the medical literature to date. The urachus is a primitive structure which before birth connected the bellybutton and the bladder.
    