The relatively well-differentiated, estrogen-receptor-positive breast cancer cell lines MCF7 and MCF10Ca1h had ∼10% SORE6+ cells, while the more malignant MCF10Ca1a and the highly aggressive MDA-MB-231 cells had an increasingly higher representation of SORE6+ cells in the culture (Figure 1G). This evidence concerns the gene ESR1 and breast carcinoma.