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Figure 1: Scheme of potential cells of origin of Merkel cell carcinoma (MCC), shown from an ontogenetic perspective. All arrows with a scattered  line represent thus far hypothetic lineage relationships. However, whereas MCC derivation from Merkel cells is not very likely, there are hints implying epidermal stem cells in MCC genesis, and dermal stem cells as well as SKPs at least cannot be excluded as cells of origin for MCC. For each putative cell type of origin, an involvement of MCPyV in MCC genesis is highly probable, at least in a large fraction of MCCs.