Merkel cell carcinoma (MCC) is a cutaneous neuroendocrine malignancy that exhibits clinically aggressive features and is associated with a poor prognosis. Ultraviolet (UV) radiation may be a cause, and corresponds with the sites of these tumours, often on sun-exposed skin, mostly (94%) in the White population. UV light may exert local immunomodulating action as it decreases amount of epidermal T cells and Langerhans cells, inducing hapten tolerance. Additionally, UV- specific mutations in TP53 and Harvey (Ha)-RAS genes are present in some MCC cell lines. Recently, the polyomavirus group has been linked with MCC. The MCC polyomavirus (MCPyV) has been isolated from MCC tissue and thought to be present in up to 80% of MCC. Tumorigenesis likely is caused by a number of sequential steps from viral integration into host DNA, mutagenic events, and specific immune responses.
