Detection of Merkel cell polyomavirus and human papillomaviruses in Merkel cell carcinoma combined with squamous cell carcinoma in immunocompetent European patients.

Background: About 10% of patients with Merkel cell carcinoma (MCC) suffer from an associated squamous cell carcinoma (SCC). In European patients, Merkel cell polyomavirus (MCPyV) is detectable in 60%-88% of the MCC tumors. In combined lesions, MCPyV was not detectable so far.
Methods: We investigated 2 combined tumors of MCC and SCC for the presence of MCPyV and human papillomavirus (HPV) by polymerase chain reaction and immunohistochemistry.
Results: In both lesions, MCPyV DNA was found, and in 1 case, HPV DNA was also detected. This is the first report of a coinfection with HPV and MCPyV in combined MCC-SCC tumors.
Conclusions: The results underline the hypothesis of co-cancerogenesis of 2 oncogenic viruses in nonmelanoma skin cancer. Technical reasons and a low viral copy number of MCPyV hampering immunohistochemical detection may be responsible for the negative results in the literature.