Immunohistological studies on clinically silent pituitary adenomas

Clinically inactive adenomas represent 30.7% of all pituitary tumors in our surgical collection of 616 cases. Ninety-six tumors were studied immunohistologically with many antibodies for their hormone content. Morphological classification of these adenomas reveals oncocytic adenomas in 42 cases (44%), small cell chromophobe adenomas in 33 (34%), large cell chromophobe adenomas in 14 cases (15%), undifferentiated mucoid cell adenomas in 4 cases (4%) and undifferentiated acidophil adenomas in 3 cases (3%). Immunohistological studies performed with the six pituitary hormones GH, prolactin, ACTH, TSH, LH and FSH and additionally with α-subunit demonstrated nearly all possible combinations of hormones in adenoma cells. The most frequently occurring (29%) was LH (in 3% of adenomas alone); α-subunit followed in frequency (24%), with FSH present in 21%. Combinations of 2 hormones were detected in 16%, of 3 in 13% and of more than 3 hormones in 2%. All 6 hormones and α-subunit were negative in 48% of adenomas. It must be concluded 1) that many clinically silent adenomas are LH- or FSH- or α:-subunit-positive and therefore probably originate from gonadotropic cells, and 2) that clinically silent adenomas of acidophil cell type or mucoid cell type are rare. Although many of these adenomas apparently do not secrete the hormone which they immunohistologically contain, determining the plasma levels of the gonadotropins, and especially the α-subunit in clinical studies, may obtain a suitable and helpful clinical marker in the diagnosis of “endocrine inactive” adenomas, and especially of their recurrences.