To better understand the consequences of this genetic aberration, we first surveyed conditionally reprogrammed cell lines from PDXs from triple-negative breast cancer patients harboring loss of one allele of CTCF (SI Appendix, Fig. S1A) and with CTCF expression equivalent to, or lower than in, our previously established CTCF+/− MCF10A mammary epithelial cell line harboring a KO of one CTCF allele (21) (Fig. 1A). The gene discussed is CTCF; the disease is triple-negative breast carcinoma.