KRT14 and Merkel cell skin cancer: Spurgeon et al. also reported that when tumor-derived genomic T antigen (both sT and MCC-derived truncated LT) is expressed under a constitutive K14 promoter in FVB/N background mice (K14-MCPyV168), two-thirds of mice are viable, whereas the rest of the mice died or were euthanized at early age due to malnourishment [17].