Gastrointestinal Neuroendocrine Tumors: Concordance Of Sst2 And Chromogranin A Immunohistochemical Staining In Relation To Primary Site Of Tumor Origin: A Single-Center Retrospective Analysis

e21102 Background: Previous analyses have demonstrated that a neuroendocrine tumor's site of origin correlates with tumor biology, clinical presentation, and oftentimes prognosis. There is however limited data available on the concordance of SST2 and Chromogranin A immunohistochemical staining in relation to primary site of tumor origin. Methods: We sought to determine the concordance of IHC staining for SST2 and Chromogranin A, with site of tumor origin. We retrospectively analyzed 78 formalin-fixed, paraffin-embedded neuroendocrine tumor (NET) specimens that had undergone immunohistochemical staining (IHC) for SST2 and Chromogranin A (ChrgA). IHC staining was graded 1+ to 3+ for both SST2 and ChrgA. Results: There were a total of 78 gastrointestinal tumor specimens. The two sites of primary origin included small bowel (55/78), and pancreas (23/78). Conclusions: Our results obtained by the semi-quantitative assessment of SST2 and ChrgA by IHC staining, demonstrates the likelihood of concordance in SST2 and ChrgA in pancreatic NETs. Although small bowel NETs were most often ChrgA 2-3+, there was marked heterogeneity in terms of SST2 IHC staining and thus a lack of concordance between the two neuro-peptide markers. Immunohistochemical staining by site of primary origin Small bowel NETs 1+ 2+ 3+ Neg SST2 40% 29% 25% 6% ChrgA 4% 7% 89% 0% Pancreatic NETs SST2 13% 44% 35% 8% ChrgA 9% 13% 74% 4% No significant financial relationships to disclose.