Merkel cell polyomavirus (MCPyV) DNA has been detected by PCR in 75-100% of Merkel cell carcinomas (MCC), an aggressive neuroendocrine skin cancer. MCPyV is a 5.4 kb DNA virus that expresses tumor (T) antigen in tumor tissues. The aim of this study was to analyze which subset of MCC is biologically associated with MCPyV using various viral detection methods.

Genomic DNA isolated from paraffin-embedded tissue of 61 MCC was analyzed by MCPyV-specific PCR. Using a 5kb MCPyV DNA probe, the physical status of MCPyV was determined by fluorescence in situ hybridization (FISH) using tyramide signal amplification and ApoTome microscopy. Expression of large T antigen was assessed by immunohistochemistry (IHC) using monoclonal antibody CM2B4 (kindly provided by Y. Chang).

A total of 44 of 61 (72%) MCC were positive for MCPyV by PCR. 34 of these 44 cases (77%) were also positive for MCPyV by FISH and 28 (64%) showed strong nuclear large T antigen expression by IHC. In contrast, none of the 17 PCR-negative tumors showed FISH signals and only 1 case showed a weak immunostaining for large T antigen. FISH analysis showed in 16 cases (47%) tumor nuclei with a single punctate signal indicating viral integration. In 8 of these tumors also areas were observed with a granular pattern with >1 nuclear signals varying significantly in size and intensity, indicating the presence of episomal viral DNA and/or RNA. In the remaining 18 cases (53%) an exclusive granular FISH pattern was observed.

Our data indicate that a subset of MCC is caused by MCPyV as determined by PCR, FISH and IHC analysis (46% is positive with all 3 detection methods). FISH and IHC showed a strong positive and negative concordance. FISH signal evaluation furthermore suggests viral integration in half of the positive MCC and a non-clonal viral persistence in the remaining positive cases. Further studies have to validate these findings and elucidate the molecular mechanisms underlying MCV-positive and -negative MCC development.

Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5352.