The causes of pituitary tumors are unknown. A tumor of the anterior pituitary can cause excess growth hormone production, leading to gigantism or acromegaly. Too much thyroid-stimulating hormone can lead to hyperthyroidism, and excess adrenocorticotropic hormone can cause Cushings Syndrome. Finally, an increased production of prolactin can cause galactorrhea, absence of menstrual periods, and infertility in women. In men, increased production can cause impotence, infertility, feminization, and galactorrhea.