Significant overexpression of the Merkel cell polyomavirus (MCPyV) large T antigen in Merkel cell carcinoma.

BACKGROUND: The purpose of this study was to determine the expression pattern of the Merkel cell polyomavirus (MCPyV) large T-protein antigen in patients with Merkel cell carcinoma.

METHODS: A tissue microarray (TMA) containing 30 specimens was constructed and stained for the MCPyV large T protein. Immunohistochemical expression was determined semiquantitively and was compared to patients' outcome.

RESULTS: Nuclear expression of MCPyV large T protein was detected in 29 of 30 specimens (97%). In particular, 60% to 100%, 30% to 60%, and 10% to 30% of tumor cells were positive in 27 specimens (90%), 1 (3%), and 1 (3%), respectively. There was no difference in positivity between primary and metastatic lesions. Clinical data could not be correlated to MCPyV large T-protein expression.

CONCLUSION: MCPyV large T protein was significantly overexpressed in 97% of all specimens. Although we could not demonstrate a predictive effect, MCPyV large T protein may represent a molecular marker with utility in pathological diagnosis as well as a potential new therapeutic target in patients with Merkel cell carcinoma.