PRL and pituitary tumor: PRL deficiency, or hypoprolactinemia, consists of very low or undetectable PRL levels deriving from a pituitary dysfunction caused by genetic causes, or acquired from pituitary tumors, neurosurgery, pituitary irradiation, chemotherapy, infiltrative disorders, autoimmune diseases, traumatic brain injuries, vascular damage, and drugs, as is the case of any isolated pituitary deficiency [54].