CTCF and cancer: By now, the enrichment of mutations in many regulatory regions has been linked to cancer development, including mutations in estrogen receptor binding sites in breast cancer (1), recurrent microdeletions in CCCTC-binding factor (CTCF) binding sites involved in chromatin organization, which lead to a deregulation of oncogenes in T-cell acute lymphoblastic leukemia (2), and mutations in other transcription factor binding sites (3).