111In-pentetreotide (somatostatin analogue) scintigraphy as an imaging procedure for endocrine gastro-entero-pancreatic tumors.

It was the aim of the present study to examine whether 111In-pentetreotide, a somatostatin analogue with predominantly renal excretion, is a suitable receptor agonist for scintigraphic imaging of endocrine gastro-entero-pancreatic (GEP) tumors, and to evaluate the contribution of the usual imaging times 4 and 24 h p.i. In 36 patients, planar scintigrams obtained 4 h, and 24 h after i.v. injection of 111 or 222 MBq 111In-pentetreotide were compared to the results of other imaging procedures and of surgery. Single photon emission computed tomography (SPECT) was also performed 24 h p.i. Positive scintigraphies were obtained in 32 out of 36 patients (18/19 patients with carcinoid syndrome, 8/9 with non hormone-producing endocrine GEP tumors, 2/4 with gastrinomas, 1/1 with glucagonoma, 1/1 with a VIPoma, 2/2 with paragangliomas). In 9 patients tumor manifestations previously not detected by conventional imaging procedures were disclosed by 111In-pentetreotide scintigraphy. 24-h images yielded significantly more true positive findings than 4-h images. In 4 patients liver metastases missed on planar scans were detected by SPECT. A discrepancy between patient-based and organ-based analysis of the results was encountered thus indicating a possible intraindividual heterogeneity in somatostatin receptor expression. In conclusion, 111In-pentetreotide is a suitable somatostatin analogue for scintigraphic in vivo demonstration of somatostatin receptors and for imaging of most tumor manifestations in patients with endocrine GEP tumors. Further studies will have to evaluate whether or not a positive receptor scintigraphy predicts response to treatment with long-acting somatostatin analogues.