Below is an instruction from Human. Write a response.
    ### Instruction:
    What causes Merkel cell carcinoma ?
    ### Response:
    What causes Merkel cell carcinoma? The exact underlying cause of Merkel cell carcinoma (MCC) is unknown, but several risk factors have been associated with the development of MCC. Having one or more risk factors does not mean that a person will develop MCC; most individuals with risk factors will not develop MCC.
    