Immunohistological determination of beta-endorphin in chromophobe, clinically hormone-nonproducing hypophyseal adenomas

Pituitary adenomas are usually classified according to the nature of their proper hormonal production. Silent adenomas of the pituitary are tumors without clinical and biochemical evidence of overproduction of any known adenohypophyseal hormones. The proportion of such seemingly nonfunctioning tumors is 20 to 30%. Silent corticotropic adenomas are able to synthesize some normal or abnormal sequences of proopiomelanocortin precursor without any signs of hypercorticism. These tumors were divided into basophilic adenomas with strong periodic acid-Schiff (PAS) positivity and chromophobic adenomas with moderate or no PAS positivity. All of our cases were chromophobic adenomas. Two of the cases were positive for beta-endorphin by immunofluorescence. ACTH immunoreactivity was not present in the cells. Electron microscopic study of the adenoma cells showed small secretory granules with a halo. The diameter of these granules varied from 50 to 250 nm. Automated morphometric and densitometric investigations of silent corticotropic adenomas and adenomas from patients with Cushing's disease gave different karyometric results. The most important practical problem arising from the present investigation was the high frequency of recurrence of silent corticotropic tumors.