Among these, five AS changes (RBM27 exon 13; PIP5K1A exon 13; N-PAC exon 5; MARK2 exon 15, and PEX26 exon 4) were also observed—to different extents—in MDA-MB-231 and BT549 cell lines, thus suggesting their independence from the ER status of the breast tumor, whereas for seven events (ADD3 exon 13, MAP3K7 exon 12, MARK3 exon 16, PACSIN2 exon 8, FGFR1OP2 exon 4, and, with a less marked splicing change, DIAPH1 exon 2, LMO7 exon 9), an aberrant AS profile was found only in ER-positive breast cancer cells (Figure S1). Here, ADD3 is linked to breast cancer.