Non-functioning gastroenteropancreatic (GEP) tumors: a 111In-Pentetreotide SPECT/CT diagnostic study

In a retrospective study performed in non-functioning GEP tumor patients we further investigated 111In-Pentetreotide SPECT/CT usefulness in diagnosis, staging and follow-up also evaluating whether the procedure may give more information than conventional imaging procedures (CIP), such as CT, MRI, US. We enrolled 104 consecutive patients with non-functioning GEP tumors, 30 in initial diagnosis and staging phases (IDS) and 74 in follow-up (FU). All patients underwent somatostatin receptor scintigraphy (SRS) whole body scan at 4, 24 and, if necessary, 48 hours followed by abdominal and chest SPECT/CT after 111In-Pentetreotide 148-222 MBq i.v. injection. The patients previously underwent 2 to 3 CIP. At both CIP and SPECT/CT, 34/104 patients were classified as no evidence of disease (NED); in 70/104 patients, neoplastic lesions were ascertained and 12 IDS and 17 FU were classified as not operable and treated with octeotride or chemotherapy. SPECT/CT and CIP were concordantly positive in 44 patients, while only CIP was positive in 6 cases and only SPECT/CT in 20. Both per-patient sensitivity and accuracy of SPECT/CT (91.4 and 94.2%, respectively) were higher than CIP (71.4 and 80.8%, respectively), but not significantly. Globally, 292 lesions were ascertained: 141 hepatic, 78 abdominal extra-hepatic and 73 extra-abdominal. CIP detected 191/292 (65.4%) lesions in 50 patients, while SPECT/CT 244/292 (83.6%) in 64, the difference being significant (p<0.0001). No false positive results were found at both SPECT/CT and CIP. Both SPECT/CT sensitivity and accuracy were higher than CIP in G1, G2, neuroendocrine carcinoma (NEC) and mixed adeno-neuroendocrine carcinoma (MANEC) patients, but significantly only for G1. Globally, SPECT/CT incremental value than CIP was 35.6%. SPECT/CT correctly modified CIP classification and patient management in 27.9% of cases, while it down-staged the disease than CIP in 9.6% of cases. However, the two procedures combined use could achieve the highest accuracy value. 111In-Pentetreotide SRS, acquired as SPECT/CT, showing high sensitivity and accuracy values, more elevated than CIP in the present study, can still have a wide employment in the routine diagnostic protocol of non-functioning GEP tumors with significant impact on patient management and therapy planning. The procedure is simple to perform, has limited cost and wide availability in all Nuclear Medicine Centers.