8785 Does Somatostatin Receptor Expression Intensity Impact Prognosis in Non Pituitary Neuroendocrine Tumors Treated with Somatostatin Analogues?

Abstract Disclosure: N. Saleh Jouneghani: None. S. Fazeli: None. S. Chang: None. A. Hosseini: None. R. Marandi: None. A. Siddiqui: None. M. Talley: None. B. Salehian: None. Does Somatostatin Receptor Expression Intensity Impact Prognosis in Non Pituitary Neuroendocrine Tumors Treated with Somatostatin Analogues? Introduction: Non-pituitary neuroendocrine tumors (NETs) show different somatostatin receptor subtype (SSTR) expression, but their role in tumor progression and prognosis is not well known. We hypothesized that NETs with higher expression of SSTR2, SSRT5, or co-expression of SSTR2 and SSTR5 will have better outcome when treated with Somatostatin Analogues (SSA). Method: Retrospectively, patients with non-pituitary neuroendocrine tumors, followed for more than one year between 1985 and 2022, and treated with SSA (Octreotide or Lanreotide) who had available tissue were selected. Tissue immunostaining performed for SSTR2 and SSTR5 with use of monoclonal antibodies. Expression analysis of the SSTR2 and SSTR5 were evaluated by the validated semi-quantitatively method, reported by an intensity score of 0 -3. The progression free survival and overall survival were calculated by Kaplan Meier and compared in different subgroups with SSTR expression intensity. Response evaluation was assessed using RECIST v1.1. Results: Of 279 non-pituitary neuroendocrine tumors, 51 meet the criteria and tissue sent for analysis. The median age at diagnosis was 62; male 49%, with median follow up 7 years, 85% stage IV at diagnosis, most common primary tumor was in gut 54% followed by pancreas 33%. Positive SSRT5 tumors had 93% SSRT2 co-expression. There were no significant differences in progression-free survival (PFS) observed between tumors with low or high SSTR2 intensity expression (P=0.62). The presence or absences of SSRT5 expression did not have any impact on PFS (p=0.57) or overall survival (p=0.3). Conclusion: in the patient with non-pituitary neuroendocrine tumors, higher SSTR2 expression intensity or having SSRT5 co-expression, did not correlate with a better PFS or overall survival in response to SSA, in our study. Further prospective studies are needed to clarify if higher expression intensity of SSRTs correlates with better response to SSAs in NETs. Presentation: 6/1/2024