SOX9 and Merkel cell skin cancer: In this study, we aimed to shed further light on the possibility that a subset of MCC tumors arise from epithelial stem cells of the skin by examining the expression of cytokeratin-19 (CK19), leucine-rich repeat-containing G-protein coupled receptor 5 (LGR5), and SRY-box transcription factor 9 (SOX9), markers of hair follicle stem cells [21–23], as well as leucine-rich repeats and immunoglobulin-like domains protein 1 (LRIG1), a marker of both hair follicle stem cells and stem cells of the interfollicular epidermis [24, 25], in MCC and normal human skin.