KRT20 and Merkel cell skin cancer: Second, molecular analysis was done on archival tumor tissue, which was obtained at different time points in relationship to the clinical history; there was no information regarding the status of the patients, whether the tumors were primary or metastatic, the location of the tumor and the presence or absence of Merkel cell polyomavirus, or cytokeratin-20 positivity (found in most, but not all, Merkel cell cancers) [95].