Improved detection suggests all Merkel cell carcinomas harbor Merkel polyomavirus.

A human polyomavirus was recently discovered in Merkel cell carcinoma (MCC) specimens. The Merkel cell polyomavirus (MCPyV) genome undergoes clonal integration into the host cell chromosomes of MCC tumors and expresses small T antigen and truncated large T antigen. Previous studies have consistently reported that MCPyV can be detected in approximately 80% of all MCC tumors.