Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Prolactinoma ?
    ### Response:
    A prolactinoma is a benign noncancerous tumor of the pituitary gland that produces a hormone called prolactin. Prolactinomas are the most common type of pituitary tumor. Symptoms of prolactinoma are caused by hyperprolactinemia --- too much prolactin in the blood --- or by pressure of the tumor on surrounding tissues.
    