Below is an instruction from Human. Write a response.
    ### Instruction:
    What causes Pilomatrixoma ?
    ### Response:
    What causes a pilomatrixoma? The exact underlying cause of pilomatrixoma is not well understood. Changes (mutations) in the CTNNB1 gene are found in at least 75% of isolated (without other signs and symptoms) pilomatrixomas. These mutations are somatic, which means they are not inherited and are only present in the tumor cells.
    