Is There an Additional Value of Using Somatostatin Receptor Subtype 2a Immunohistochemistry Compared to Somatostatin Receptor Scintigraphy Uptake in Predicting Gastroenteropancreatic Neuroendocrine Tumor Response?

Background and Aims: It is unknown whether tumoral somatostatin receptor subtype 2a (sst 2a) immunohistochemistry (IHC) has additional value compared to somatostatin receptor scintigraphy (SRS) uptake using OctreoScan (R) in predicting response to peptide receptor radiotherapy using Lu-177-octreotate (PRRT) in patients with gastroenteropancreatic neuroendocrine tumors (GEP-NETs). The aims of this study were: (1) to establish the percentage of sst 2a immunopositivity in GEP-NET samples of PRRT-treated patients, (2) to determine the relationship between best GEP-NET response using RECIST 1.0 criteria 1 year after PRRT and tumor-al sst 2a IHC, and (3) to compare characteristics of patients with sst 2a IHC-negative and -positive tumors. Methods: All 73 consecutive patients were selected for PRRT based on a positive SRS. Radiological response was scored according to RECIST 1.0 criteria. sst 2a status was detected on tumor samples by IHC. Results: In total, 93% of GEP-NET samples showed sst 2a IHC positivity. No statistically significant relationship was observed between in vitro sst 2a expression and in vivo best GEP-NET response 1 year after PRRT (p = 0.47). Sex, primary tumor site, disease stage, ENETS TNM classification, Ki-67 index, highest serum chromogranin-A level, and highest neuron-specific enolase level were not significantly different between patients with negative and positive sst 2a tumoral IHC with the exception of age at diagnosis (p = 0.007). Conclusions: sst 2a IHC of tumor samples has no additional value compared to SRS uptake using OctreoScan (R) in predicting tumor response after PRRT. (C) 2015 S. Karger AG, Basel