Merkel cell polyomavirus in cutaneous squamous cell carcinoma of immunocompetent individuals

Squamous cell carcinoma (SCC) is the second most frequently diagnosed skin cancer. It has a higher incidence in immunosuppressed individuals such as organ transplant recipients and human immunodeficiency virus (HIV) carriers. Recently, a newly described polyoma virus, Merkel cell polyomavirus (MCPyV), was found in Merkel cell carcinoma (MCC), a rare aggressive skin cancer also associated with immunosuppression. We hypothesized that MCPyV would be present in SCCs. To test for the presence of MCPyV in immunocompetent SCC patients, we used PCR primer sets directed against the large T (LT) antigen and VP1 gene of MCPyV. We detected MCPyV in 15% (26/177) of SCC DNA samples and 17% (11/63) of adjacent skin DNA samples from 21 of 58 (36%) individuals studied. We did not detect MCPyV in any matched normal blood DNA (0/57), but observed the presence of MCPyV DNA in 1 of 12 normal mouthwash DNAs. All sequenced SCC samples had a common mutation truncating the LT antigen that provides indirect evidence of viral integration. The presence of MCPyV in approximately 15% of SCCs from immunocompetent individuals warrants evaluation of MCPyV as an etiologic agent in the carcinogenesis of SCC.