Assessment of somatostatin receptor expression in the management of

Objectives Somatostatin receptor scintigraphy (SRS) and represents the criterion of choice for treatment with somatostatin analogs gastro-entero-pancreatic neuroendocrine tumors (GEP-NETs). Immunohistochemistry (IHC) is a reliable and validated method for the detection of somatostatin receptors (SSTRs). We retrospectively compared the sensitivity of IHC and SRS in the assessment of SSTRs expression in patients affected by GEP-NETs.

Methods Patients attending our hospital from 1997 to 2007 were selected. Inclusion criteria required availability of tumor specimens and SRS preformed as a standard staging procedure. The IHC analysis was restricted to SSTR2 and SSTR5. A comparison between the sensitivity of IHC and SRS in the detection of SSTRs expression was performed. 25 out of 44 patients were male, 19 female. Sites of origin were: 15 pancreas; 9 unknown; 7 ileum; 6 stomach; 3 colon; 2 rectum; 2 duodenum. 13 patients had localized disease, 31 had metastatic tumors.

Results 24/44 patients (55%) had a foregut carcinoid, 9 (20%) a midgut carcinoid, 2 (5%) a hindgut carcinoid and 9 (20%) an unknown primary site GEP-NET. 37 patients (84%) were found to express SSTRs. SRS detected SSTRs expression in 28 (63%) patients. IHC detected SSTRs expression in 34 (77%) patients. The sensitivity of SRS was 76%. The sensitivity of IHC was 92%. SSTR2 was expressed in 50% of tumours not visualized by SRS.

Conclusions Although not statistically significant, SRS showed a lower sensitivity in detection of SSTRs expression, when compared with IHC. Tumor uptake at SRS could underestimate SSTRs expression, cutting off a significant amount of patients who could benefit from a somatostatin analogs-based treatment.