Somatostatin receptor scintigraphy in liver metastasis detection from gastroenteropancreatic neuroendocrine tumors

In patients with gastroenteropancreatic (GEP) neuroendocrine tumors, we investigated the usefulness of somatostatin receptor scintigraphy (SRS) in the detection of liver metastasis, which represents the most important prognostic factor in these tumors, and in the management of affected patients. Methods: We enrolled 149 patients with GEP tumors, 69 during initial staging and 80 in follow-up. All patients underwent whole-body scanning at 4 and 24 h, followed by abdominal planar and SPECT imaging after intravenous injection of 250 MBq 111Inpentetreotide. The patients had previously been submitted to 2 of 3 conventional imaging procedures (CIP), such as CT, MRI, and ultrasound of the abdomen within 1 mo before SRS; on the basis of liver CIP data, the patients had been classified into 3 groups as follows: no evidence of liver metastases, the presence of resectable metastases, or the presence of nonresectable metastases. Results: Liver metastases were histologically proven in 65 cases. SPECT identified malignant lesions in 60 of 65 patients with metastases (sensitivity, 92.3%), planar imaging identified malignant lesions in 38 of 65 patients (sensitivity, 58.5%), and CIP identified malignant lesions in 52 of 65 patients (sensitivity, 80%). Only SPECT demonstrated liver involvement in 13 patients, whereas CIP showed liver involvement in 5 other cases. Moreover, SPECT was significantly more sensitive than planar imaging and CIP in identifying patients with single lesions. Neither SPECT nor planar imaging showed false-positive results in patients with no evidence of liver metastases, including 21 patients with hemangiomas (specificity, 100%), 12 of which were false-positive on CIP (specificity, 85.7%). SPECT per-lesion sensitivity (92.4%) was significantly higher than that of planar imaging (52.4%) and CIP (79.4%). Moreover, SPECT correctly changed patient classification and, thus, management in 28 of 149 patients (18.8%), whereas planar imaging changed classification in 13 patients (8.7%), identifying new or additional metastases not evident on CIP or excluding metastases on CIP of patients with false-positive findings, thus avoiding unnecessary surgery; however, SPECT classification was incorrect in 3.3% of patients, and planar imaging was incorrect in 17.4%. Conclusion: 111In-Pentetreotide SRS is a useful diagnostic tool in the detection of liver metastases in GEP tumor patients. In particular, SPECT proved to be significantly more sensitive and accurate than both planar imaging and CIP. Moreover, SPECT was also the most reliable procedure to obtain correct patient classification, thus guiding the most appropriate therapeutic strategy.