Somatostatin receptor SSTR2A and SSTR5 expression in neuroendocrine breast cancer

Neuroendocrine breast cancer (NEBC) is a group of rare tumors, which could benefit from therapy targeting the somatostatin receptors (SSTRs). In particular, SSTR2A and SSTR5 are potential targets given their consistent expression in gastrointestinal and pancreatic primary and metastatic neuroendocrine cancers. Currently, there are no studies describing the expression of SSTRs in NEBC. The purpose of our study was to characterize the immunohistochemical expression of SSTR2A and SSTR5 in a cohort of NEBC. Thirty-one primary NEBC cases were analyzed, and SSTR2A and SSTR5 immunohistochemistry performed and scored using the modified immunoreactive score proposed by Remmele and Stanger. All patients were females with a mean age of 66.6 years (SD = 14). 77% of cases were histological grade 2. SSTR2A showed a weak positivity in 11 cases (35.5%), moderate positivity in 6 cases (19.4%) and strong positivity in 5 cases (16.1%). Nine cases were negative for SSTR2A (29%). SSTR5 showed a weak positivity in 16 cases (51.6%), moderate positivity in 6 cases (19.4%), while no cases showed strong positivity. Nine cases were negative for SSTR5 (29%). Five cases were negative for both SSTR2A and SSTR5. A weak to moderate SSTR2A and SSTR5 expression was observed in 50-70% of the cases. A subset of NEBCs with strong SSR2A expression may benefit from SSTRs targeted therapy. These results need further validation in a larger series including metastatic NEBC, to provide potential therapeutic targets for patients with advanced disease.