Expression of Merkelcell polyomavirus (MCPyV) large T-antigen in Merkel cell carcinoma lymph node metastases predicts poor outcome

BACKGROUND The aim of this study was to determine the prevalence of MCPyV in Merkel cell carcinoma (MCC) primaries versus lymph node metastasis and to evaluate possible prognostic factors. METHODS Samples of MCC primaries and lymph node metastases were stained immunohistochemically for the MCPyV large T-antigen and expression was compared to patients´ clinical outcome. RESULTS 41 MCC patients were included. 33 (61%) out of 54 specimens were MCPyV-positive in the immunohistochemistry. 15 (47%) out of 32 primary tumors were positive compared to 18 (82%) out of 22 lymph node metastases. Eleven patients with positive polyomavirus expression died from the carcinoma compared to 4 patients without virus expression. Cox regression analysis showed worse disease-free survival in patients with MCPyV compared to virus-negative lymph nodes (p = 0.002). CONCLUSIONS To our knowledge this is the first study to describe a negative prognostic effect of the MCPyV expression in lymph node metastasis in MCC patients.