CTCF and breast cancer: In the MCF7 human breast cancer cell line, where a large percentage of CTCF-independent cohesin binding sites were previously reported (22), we observed robust correspondence between CTCF and RAD21 (a subunit of cohesin) binding at the single-locus (Fig. 1B) and genome-wide scales, with 90.7% of RAD21 peaks overlapping CTCF binding sites (SI Appendix, Fig. S1A).