Somatostatin receptor scintigraphy with 111In-pentetreotide in non-functioning gastroenteropancreatic neuroendocrine tumors

To investigate somatostatin receptor scintigraphy (SRS) usefulness compared to conventional imaging procedures (CIP) in non-functioning gastroenteropatic (GEP) neuroendocrine tumors, we studied 40 patients, 30 in follow-up (FU) after previous operation for primary tumor (27 cases) or non-operable for disseminated metastases (3 cases), and 10 in the phase of initial diagnosis and staging (IDS). All patients were asymptomatic for hormone overexpression, with slightly high serum chromogranine A in 6 FU. The definitive diagnosis was obtained by surgery, laparotomy or percutaneous CT/US guided biopsy. Within 1 month before scintigraphy, all patients had undergone at least 2 of 3 CIP (CT, MRI and US); 4 and 24 h after 250 MBq 111In-pentetreotide i.v. injection, whole body scanning, planar and SPECT over the abdomen or other suspect regions were performed. Globally, 135 neoplastic lesions (84 hepatic, 34 abdominal extra-hepatic and 17 extra-abdominal) were ascertained in 32/40 patients; SPECT was positive in 29 cases, CIP in 28 and planar in 20, while all 3 procedures were true negative in the remaining 8 cases. Per patient sensitivity and accuracy were significantly higher at SPECT and CIP than planar. SPECT showed a significantly higher per lesion sensitivity (89.6%) than CIP (72.6%) and planar (53.3%) while CIP sensitivity was significantly higher than planar. SPECT correctly modified CIP patient classification and thus management in 18.7% of patients, while it downstaged the disease in 9.4% in respect of CIP; planar was incorrect in 51.3% of cases. SPECT and CIP combined use achieved 100% accuracy and correctly classified all patients. 111In-pentetreotide SRS, particularly SPECT, is a useful diagnostic tool in the detection of non-functioning GEP tumors, contributing to correct patient classification and appropriate therapeutic strategy. SPECT proved more sensitive than CIP, but their combined use achieved the highest accuracy values and gave the most accurate disease staging.