Endocrine Abstracts (2008) 16 P274

Variability in rensponse to octreotide in patients with insulinoma detected by 111In-octreotide scintigraphy (Octreoscan)

Fabrizio Diacono & Guido Tamburrano

University Sapienza, Rome, Italy.

Purpose: 111In-octreotide scinti aphy may be useful in patients with insulinoma during pre-surgical localization of the tumor and octreotide is effective in inhibiting insulin secretion and reducing the hypoglycemic events. The aim of the study was to evaluate 111in-octreotide scintigraphy in localizing primary and metastatic insulinomas and predicting the response to octreotide administration.

Patients and methods: Diagnosis of insulinoma was made in 17 subjects (M/F 9/8; aged 41.8±15.3 years) based on hyperinsulinemic hypoglycemia (mean IRI/BG ratio 0.91±0.23) during a 72-h fasting test and confirmed by surgical procedure (mean tumor diameter 1.3±0.4 cm). One patient had a malignant insulinoma. All patients had Octreoscan. Blood glucose and serum insulin were measured fasting and at 20, 40, 60, 80, 100, 120, 140, 160, 180 minutes during intravenous infusion of octreotide at a rate of 100 μg/hour for three hours (Intravenous Octreotide Suppression Test); response was considered: ‘good’ when mean insulin secretion during the test was suppressed over 50% of basal value, ‘fair’ when it was suppressed between 20 and 49%, and ‘absent’ when suppression did not reach the 20% of basal value.

Results: Octreotide inhibited insulin secretion in 14 on 17 patients (overall results: mean basal insulin 36.8±31.2 μUI/ml, mean insulin during the test 13.5±7.6 μUI/ml – P<0.05). Fifteen on 17 (88%) pancreatic insulinomas and 1 liver metastasis were localized with Octreoscan, among these patients 12 (80%) were responders (3 good responses and 9 fair responses) and 3 (20%) were non responders. Malignant insulinoma had a good response. The rate of suppression ranged from 0% to 84.1% (mean rate 34.7±25.2%).

Conclusions: According to the study 80% of insulinomas detected by 111In-octreotide scintigraphy may respond to octreotide administration with a very variable rate of inhibition of insulin secretion.

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