Pituitary adenomas of the multiple endocrine neoplasia type I syndrome.

In a series of 1,500 pituitary adenomas surgically resected at Mayo Clinic, 41 (2.7%) occurred in the setting of multiple endocrine neoplasia, type I (MEN-I). Of the 40 patients (18 males, 22 females), 21 (52%) presented with clinical evidence of a pituitary neoplasm, 13 with hyperparathyroidism, and two with functional islet cell tumor. Of the 41 tumors, 11 (27%) were microadenomas, and 30 (73%) were macroadenomas. Immunocytochemical studies demonstrated the following reactivities: GH (4), GH/PRL (6), GH/PRL/glycoprotein (7), GH/ACTH/glycoprotein (1), PRL (16), PRL/TSH (1), ACTH (3), and null cell adenoma (3). We conclude that, in comparison with pituitary adenomas occurring in the general population, those occurring in association with MEN-I are (1) more often endocrinologically functional, (2) more frequently GH- or PRL-producing, and (3) clinicopathologically similar in terms of the subjects age and sex as well as of tumor size and invasiveness.