Because a minority of MCC expresses neither ATOH1 nor MCPyV, we performed differential gene expression analysis (DGEA) of ATOH1 CDXs compared to the entire CDX biobank and applied a Merkel cell-specific gene signature36 (Table S2), which was not significantly enriched in ATOH1 CDXs (Figure S1B), further supporting the theory that ATOH1 CDXs do not have a Merkel cell origin. This evidence concerns the gene ATOH1 and Merkel cell skin cancer.