SOMATOSTATIN RECEPTOR SCINTIGRAPHY IN PATIENTS WITH PITUITARY-ADENOMA

Presence of high-affinity somatostatin (SST) receptors in most endocri ne tumor cells allow in vivo scintigraphic visualization of these neop lasms after intravenous administration of a radionuclide-labeled somat ostatin analog. In-111-octreotide is at present the most often used su bstance for imaging of the SST receptor expression in vivo. The aim of this study is to investigate the correlation between presence of in v ivo scintigraphically detectable SST receptors in pituitary tumors and clinical parameters such as patients' age, tumor size, hormonal hyper secretion, and response to octreotide therapy Forty-two consecutive pa tients were enrolled in this trial. Twenty-five of them had nonsecreti ng pituitary tumors, 11 were acromegalic, and 6 had macro- or micropro lactinoma. Scintigraphic images of the head were obtained at 10 min an d 24 hours after injection of the radionuclide. In 23 patients, no spe cific binding of In-111-octreotide was found. Five patients showed a w eak positive, 5 had a positive, and 9 a strong positive signal in the region of interest. Uptake of octreotide was significantly correlated with tumor size and age (p < 0.01). Small-size pituitary adenomas were most likely to be scintigraphically receptor-negative, while large su prasellar tumors tended to exhibit a rather strong receptor positivity Statistical analysis of the data could not confirm the hypothesized c orrelation between endocrine activity of the pituitary tumors and the scintigraphically proven SST receptor expression in vivo. A positive O ctreoscan was not predictive for the result of octreotide therapy.