SAT-LB24 Association of Expression of Somatostatin Receptor 2 Subtype in Non-Pituitary Neuroendocrine Tumors With Response to Treatment With Somatostatin Analogues

Abstract

Background: The WHO classification of non-pituitary neuroendocrine tumors (NETs) includes grading (Ki67 proliferation index and mitosis index) and staging, and has been shown to be associated with outcome in this patient population. Neuroendocrine tumors show different somatostatin receptor (SSTR) subtypes expression, but their role has not been considered in tumor progression and prognosis. We hypothesize patients with non-pituitary NET, whose tumor tissues have higher specific SSTR2 expression patterns will experience better outcomes when treated with Somatostatin Analogues (SSA) compared to those with lower or absent SSTR2 expression. Methods and patients: City of Hope patients with non-pituitary NET who received SSA (Octreotide and Lanreotide) for over 1 year as treatment. The progression free survival was based on imaging studies (MRI, CAT scan of index tumor) on RECIST criteria, and expression of SSTR2 on the tumor obtained by surgery at the time of diagnosis. Immunohistochemical staining with a monoclonal antibody to SSTR2 performed at core pathology lab at City of Hope. H-scoring (intensity of immunostaining and percent of SSTR2 expression) was performed by one pathologist, and divided into four categories of 0-4. Pearson Chi-square test was used to assess the correlation between the SSTR2 score and 1-year progression. Outcome Measures: The effect of SSA therapy on 1 year progression-free survival (PFS), among patients with high intensity and percent of SSTR2 expression on the resected tumor tissue was compared to those with low or absent SSTR2 expression. Patient population: Of the 297 patients identified with non-pituitary neuroendocrine tumor, 70 patients satisfied the inclusion criteria and a total of 52 patients had data that was completely available for analysis. Results: Mean age of study subjects was 61+1.8 years. 26 were female and 26 were male. The primary sites for NET were: pancreas 17, jejunum 16, ileum 9; paraganglioma and pheochromocytomas 3, lung and thymus 3, gastric 2, and medullary thyroid carcinoma 1. The one-year progression was not significantly different among those with low and absent SSTR2 compared to high expression of SSTR2. Step wise analysis based on the scoring of the SSRT2 did not show significant 1 year progression. Age was not associated with PFS. However, the need for additional therapy (liver embolization, surgical resection) was signigicantly reduced amongst patients with presence of SSTR2. Conclusion: In this preliminary study there was no significant association between SSTR2 expression and Progression free survival, however the need for additional therapy in patients on somatostatin analogues were reduced among subjects with presence of SSTR2 expression