Glycoprotein hormone α-subunit secretion in prolactinomas and in non-functioning adenomas: relation with the tumour size

OBJECTIVE Free giycoproteln hormone α-subunit plasma levels have been reported to be Increased In glycoprotein hormone-secreting adenomas and In acromegaly, but rarely In prolactinomas and In only two cases of Cushing's disease. The prevalence of elevated plasma α-subunit levels. In patients with non-functioning adenomas is still unclear. In addition, no previous work has described plasma a-subunit levels. In a comprehensive series of adenomas characterized by In-vivo secretion and/or Immunocytochemistry. PATIENTS Thirty-seven patients with definite prolactinomas and 48 with non-functioning tumours characterized by Immunocytachemistry were studied, from a series of 145 consecutive patients Including 33 acromegallcs, 18 patients with glycoprotein hormone-secreting adenomas and 9 with Cushing's disease. MEASUREMENTS Plasma free α-subunit was measured by radioimmunoassay in all patients and In a large sample of normal subjects to establish normal ranges according to sex, age and menstrual status. Tumour volume index was the product in cm³ of length, width and height of the adenoma as assessed by computerized tomography or magnetic resonance Imaging. RESULTS Twelve of the 37 (32%) patients with prolactinomas had Increased plasma a-subunit levels; their tumours were significantly larger with significantly higher plasma PRL levels than those of patients without Increased plasma α-subunit levels(P < 0·02). All prolactlnomas above 50 cm³ were associated with α-subunit secretion, whereas only 6 of 29 smaller tumours were similarly associated. Twelve of the 48 ‘non-functlonlng’ adenomas actually secreted α-subunit in vivo: 8 gonado-trophin-secreting, 2 ‘pure’α-secreting, one with negative Immunocytachemistry and one necrotic adenoma. Their volumes were significantly higher than those of adenomas without increased plasma α-subunit levels (P < 0·04). Plasma α-subunit levels were increased in the 6 patients with TSH-secreting adenomas, 8 of 12 with FSH-secreting adenomas, 11 of 33 acromegalics and none of those with Cushing's disease. CONCLUSION Plasma free α-subunit levels were Increased in 49 of 145 patients (34%). For prolactinomas and ‘non-functioning’ adenomas, α-subunit hypersecretion was seen more often with larger tumours. Half of the cases with Increased free α-subunit. In this series were patients harbouring an adenoma which did not stain for an intact glycoprotein hormone.