IN-111-OCTREOTIDE SCINTIGRAPHY IN PITUITARY-ADENOMAS

In-111-octreotide is a new tracer which allows in vivo scintigraphic e valuation of the somatostatin receptor state of several types of tumor s, including pituitary adenomas. This study reports on In-111-octreoti de scintigraphy in 20 patients with pituitary adenomas including endoc rine activity evaluation and in vitro immunohistochemical characteriza tion of the somatostatin receptor state. In-111-octreotide uptake was observed already at 4 h in 7/7 GH-secreting adenomas, in 7/7 non-secre ting adenomas and in 1/5 prolactinomas; one ACTH-secreting adenoma had no tracer uptake. Concordance between scan and histochemical results was observed in all cases. The uptake ratios evaluated at 24 h ranged from 2.3 to 4.2 showing no significant correlation with hormonal syndr omes. The following conclusions were drawn: (1) In-111-octreotide is a suitable tracer to evaluate the somatostatin receptor state of pituit ary adenomas; (2) semi-quantitative measures of tracer uptake can be e asily obtained with static planar scanning, but more refined technique s are needed for receptor kinetics evaluation; (3) the nuclear techniq ue confirms the octreotide inhibitory test in GH-secreting adenomas an d allows a unique possibility to select nonfunctioning adenomas in whi ch medical therapy with cold octreotide has a rationale.