ESR1 and cancer: Harrison et al., both in 2010 and 2013, also supported that self-renewal of BCSC is regulated by Notch signaling and added that Notch-4 knockdown has a more significant impact than Notch1 in BCSC and that Notch inhibitors operate downstream of oestrogen in the regulation of ER-negative cancer stem cells by blocking their activity and reducing their frequency [125, 126].