Mammosomatotroph Cell Adenoma of the Human Pituitary

In the morphologic study of surgically-removed pituitary adenomas, histology, electron microscopy as well as immunocytochemistry at the light microscopic and ultrastructural level were used. In material of 370 adenomas, 226 tumors (61.7%) were found to derive from the “acidophil” cell line. Thirty-one of these were densely granulated growth hormone cell adenomas; 38 were sparsely granulated growth hormone cell adenomas; 1 was composed of densely granulated prolactin cells and 114 of sparsely granulated prolactin cells. The latter represent the most common tumor type in the human pituitary. Twentyone adenomas were mixed, consisting of growth hormone cells and prolactin cells; 17 tumors were classified as acidophil stem cell adenomas. The latter are immature, aggressive neoplasms assumed to originate in the common precursor of growth hormone cells and prolactin cells.