Merkel cell carcinoma, chronic lymphocytic leukemia and other lymphoproliferative disorders: an old bond with possible new viral ties

Merkel cell carcinoma (MCC) is a rare and aggressive skin tumor. The link between tumorigenesis and immunosuppression is well known and the increased prevalence of MCC in human immunodeficiency virus carriers and organ transplant recipients and in patients with hemato-oncological neoplasias is now well recognized over the past decade. In this respect, chronic lymphocytic leukemia (CLL) seems to be the most frequent neoplasia associated with the development of MCC. Very recently, a newly described virus, the Merkel cell polyomavirus, was found in ∼80% of MCC tumor samples and is in fact the first member of the polyomavirus family to be associated with human tumors. The virus appears to play a role in the pathogenesis of MCC and may constitute the missing link between immunosuppression and the development of MCC. This review summarizes the current knowledge relating to MCC and its pathogenesis, stressing the link with hematologic neoplasias in general and to CLL in particular. We describe the permissive immunologic environment, which enables the virus-containing tumor cells to survive and proliferate in disorders like CLL. More studies are still needed to confirm this appealing theory in a more convincing manner.