As shown in Fig. 1a, high levels of Notch3 mRNA were specifically expressed in the ERα-positive luminal breast cancer cell lines MCF-7 and T-47D, but not in the ERα-negative breast cancer cell lines MDA-MB-231, BT-549 and SK-BR-3., Western blotting showed that both full-length and intracellular domain (ICD) of Notch3 were mainly expressed in luminal epithelial phenotype MCF-7 and T-47D cell lines, as shown by increased ERα and E-cadherin expression (Fig. 1b). Here, ESR1 is linked to breast cancer.