Analysis of CM7 BS junction sequences in data from total RNA-seq analysis of five BC cell lines and one non-tumorigenic breast cell line (GSE52643) revealed that 2,037 circRNAs (62.3%) were detectable in at least one cell line; of these, 36 were Differentially Expressed (DE) when comparing ER+ versus ER- cell lines (Figure 3A and Supplementary Table 4). Here, ESR1 is linked to breast cancer.