Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Kaposi's Sarcoma ?
    ### Response:
    Kaposi's sarcoma is a cancer that causes patches of abnormal tissue to grow under the skin, in the lining of the mouth, nose, and throat or in other organs. The patches are usually red or purple and are made of cancer cells and blood cells. The red and purple patches often cause no symptoms, though they may be painful.
    