Merkel cell polyomavirus in merkel cell carcinoma: clinical and therapeutic perspectives

Merkel cell carcinoma (MCC) is a rare and often aggressive cutaneous cancer with a poor prognosis. The incidence of this cancer increases with age, immunodeficiency and sun exposure. Merkel cell polyomavirus (MCPyV), a new human polyomavirus identified in 2008, is detected in the majority of the MCCs and there is a growing body of evidence that healthy human skin harbors resident or transient MCPyV. A causal link between MCPyV and MCC has been evidenced and this is the first polyomavirus to be clearly implicated as a causal agent underlying a human cancer, and MCPyV was recently classified as a 2A carcinogen. MCC is thus a rare tumor caused by a very common viral skin infection. The aim of this review is to provide a basic overview of the epidemiological, clinical, and pathological characteristics of MCC, to present the current knowledge on MCPyV polyomavirus and its causal association with MCC development, and to describe the therapeutic implications of this causal link.