TF and Merkel cell skin cancer: Furthermore, integration sites in 8 of 13 (61.5%) VP-MCC cell lines and tumors (20) coincided with VP-MCC SEs, and 6 of 13 (46.1%) were near CR TF genes, including loci regulating INSM1, ISL1, and LHX3 (Supplemental Figure 4), suggesting that these genes could have been active at the time of, or were activated by, MCPyV integration.