Mixed growth hormone and prolactin-secreting human pituitary adenomas: a pathologic, immunocytochemical, ultrastructural, and immunoelectron microscopic study.

A study of 30 adenomas from patients with signs of growth hormone (GH) and prolactin (PRL) hypersecretion revealed the presence of mammosomatotroph cells (MSC) containing both hormones in all cases. Although the number of immunostained cells varied from case to case, in 14 of 25 tumors, all stained cells were MSC. Nine tumors had the ultrastructural appearance of densely granulated growth hormone adenomas, while 11 cases resembled sparsely granulated growth hormone adenomas with frequent fibrous bodies. Exocytosis was present in six of these 11 cases, a feature unusual for pure growth hormone adenomas. Nine tumors consisted of a mixture of cells with the morphology of GH and PRL cells. In the four cases examined, immunoelectron microscopy using double immunolabeling with protein A-gold particles revealed the presence of secretory granules containing both hormones in some tumor cells recognized as mammosomatotroph cells.