Merkel Cell Polyomavirus‒Negative Merkel Cell Carcinoma Originating from In Situ Squamous Cell Carcinoma : A Keratinocytic Tumor with Neuroendocrine Differentiation
Although virus-negative Merkel cell carcinoma (MCC) is characterized by a high frequency of UV-induced mutations, the expression of two viral oncoproteins is regarded as a key mechanism driving Merkel cell polyomavirus‒positive MCC. The cells in which these molecular events initiate MCC oncogenesis have yet not been identified for both MCC subsets. A considerable proportion of virus-negative MCC i
