Interestingly, the sensitivity for the reduction in ERα levels of the different cell lines to the esiRNA treatment against MELK was significantly higher in BC cell lines expressing PR (MCF-7, T47D-1, HCC1428, BT-474, and EFM192C) (Fig. 3a,c and Supplementary Table S4), while the sensitivity for the reduction in ERα levels of the different cell lines to AP26113 (AP)-dependent ALK inhibition was significantly higher in PR-negative cells (MDA-MB-361 and ZR-75-1 cells) (Fig. 3b,c and Supplementary Table S4). Here, ESR1 is linked to breast cancer.