Background/Aims: Merkel cell carcinoma (MCC) is a rare high-grade neuroendocrine tumour of the skin. It has been speculated that MCCs express somatostatin receptors (SSTRs), but this has never been assessed in a large series of MCCs. The main aim of this study was to assess the expression of SSTR2A and SSTR5 in MCC tumours. The secondary aims were to assess whether expression of SSTR was associated with the Ki67 proliferative index, Merkel cell polyomavirus (MCPyV) status, clinical characteristics and outcome. Methods: Clinical data and tumours were collected from an ongoing cohort of French patients with MCC. Immunohistochemistry was performed with anti-SSTR2A and anti-SSTR5 monoclonal antibodies, and tumours were classified into 3 groups: ‘no expression', ‘low expression' and ‘moderate expression' using an SSTR staining score. Results: SSTR expression was assessed for 105 MCC tissue samples from 98 patients, and clinical characteristics were available for 87 of them. SSTR expression was consistent between the primary skin tumour and the corresponding metastases for SSTR2A and SSTR5 in 3/7 and 6/7 cases, respectively. SSTR2A and SSTR5 were expressed in 58 cases (59.2%) and in 44 cases (44.9%), respectively. Overall, at least one SSTR was expressed in 75 tumours (76.5%). SSTR expression was not associated with clinical characteristics, Ki67 proliferative index, recurrence-free survival or MCC-specific survival. Expression of SSTR2A was associated with MCPyV status in MCC tumours but not SSTR5. Conclusion: SSTRs were expressed in a high proportion of MCCs, although expression was heterogeneous between tumours and was not associated with disease severity.

Keywords:
Merkel cell carcinoma, Somatostatin receptor, Ki67 proliferative index, Immunohistochemistry, Outcome
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2015
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