Carcinoma, Merkel CellMerkel cell polyomavirusMerkel CellsPolyomavirus InfectionsPolyomavirusTumor Virus InfectionsSkin NeoplasmsAntigens, Viral, TumorAntigens, Polyomavirus TransformingDNA, ViralBlood Buffy CoatCarcinoma, Squamous CellCapsid ProteinsKeratin-20Polymerase Chain ReactionCarcinoma, Renal CellFacial NeoplasmsAntibodies, ViralDNA NucleotidylexotransferaseCarcinoma, Basal CellCarcinomaBK VirusImmunohistochemistry