USE OF AN ISOTOPIC SOMATOSTATIN RECEPTOR PROBE TO IMAGE GUT ENDOCRINETUMORS

Objectives: To evaluate the effectiveness of indium In 111 pentetate ( diethylenetriaminepentaacetic acid [DTPA])-D-Phe-labeled octreotide sc intigraphy in the localization of gastroenteropancreatic neuroendocrin e lesions, and to identify covert lesions, determine multicentricity, define the distribution of metastases, confirm complete removal of tum or postoperatively, and evaluate the efficacy of therapeutic embolizat ion. Design: Unmasked comparison. Setting: Tertiary care referral cent er. Patients: We studied 28 patients over a 12-month period. Biochemic al. evidence of a gastroenteropancreatic tumor was present in 13 patie nts. Octreoscan 111 was employed in four patients with an ambiguous bi ochemical diagnosis of gastroenteropancreatic tumor. Postoperative exa mination to document complete tumor removal was undertaken in seven pa tients. In one patient, Octreoscan 111 was used to evaluate the effica cy of therapeutic embolization. Intervention: [In-111] DTPA-D-Phe-octr eotide scintigraphy. Main Outcome Measure: Identification of somato-st atin receptor-bearing neuroendocrine tumors. Results: Intravenous admi nistration of [In-111]DTPA-D-Phe-octreotide followed by whole-body gam ma camera scintigraphy resulted in the localization of gastro enteropa ncreatic neuroendocrine tumors with 75% sensitivity, 100% specificity, 100% positive predictive value, 63% negative predictive value, and 82 % overall accuracy. Conclusions: While Octreoscan 111 has been shown t o localize the majority of amine precursor uptake and decarboxylation system (APUD) cell tumors as well as various other somatostatin-positi ve tumors, this technique may also be useful in a number of other circ umstances. These include prediction of tumors that will respond to oct reotide therapy, identification of covert metastases, intraoperative i dentification of tumors, and postoperative surveillance. Use of an alt ernative isotope may provide a vehicle for the administration of local therapeutic radiation to tumor cells. The precise efficacy of Octreos can 111 in the identification of lesions smaller than 3 cm with low-de nsity somatostatin-2 receptor expression remains to be determined.