Stem cells, hormones and pituitary adenomas

Pituitary tumours affect at least 10% of us, but fortunately with very few exceptions they remain occult. When they do present, either by pushing on surrounding structures such as the optic chiasm, by secreting inappropriate amounts of hormone or by causing pituitary hormone hyposecretion, their behaviour is almost always remarkably benign. About 50% of these tumours (for want of a better word) never exceed 10mm in diameter and if they do continue to grow, they almost invariably do so extremely slowly and with great modestly of malignant intent. They often remain responsive to normal hormonal signals, and have the fascinating propensity in some circumstances to behave cyclically, causing unequivocal hormonal abnormalities followed by reverting to normal before again giving rise to hypersecretion, or even resolve spontaneously. They house subpopulations of cells expressing hypothalamic hormones and dogma has it, that they are monoclonal, although recurrences often show restoration of the original chromosomal loss, making an polyclonal or at least oligoclonal initiation, with clonal dominance a possibility