Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) gastrointestinal stromal tumor ?
    ### Response:
    A gastrointestinal stromal tumor (GIST) is a type of tumor that occurs in the gastrointestinal tract, most commonly in the stomach or small intestine. The tumors are thought to grow from specialized cells found in the gastrointestinal tract called interstitial cells of Cajal (ICCs) or precursors to these cells.
    