[Pathogenesis of pituitary tumor].

Pituitary adenoma originates from adenohypophysial cells producing various pituitary hormones. Some of pituitary adenomas are associated with pathological states including primary hypothyroidism, Nelson's syndrome, hypothalamic hormone-producing tumors, multiple endocrine neoplasia type 1, McCune-Albright syndrome and transgenic animals transfected with hypothalamic hormones (HP). These facts suggest that excessive secretion of HP induces hyperplasia of the adenohypophysial cells, leading to adenoma by additive effects of other unknown factors. The majority of the pituitary adenomas are associated with de novo genetic changes in the adenohypophysial cells, which induce growth factor independent proliferation and clonal expansion of the tumor cells, due to mutation of Gsa gene, activation of hst gene, expression of growth factors (HP, AT II, bFGF), loss of heterozygosity or loss of imprinting.