As shown in Fig. 2c and Supplementary Table S4, treatment with esiRNA targeting the 11 kinases (PLK1, CDC7, AURKB, CDK1, PBK, MELK, BUB1B, PLK4, VRK1, TTK, MASTL, excluding CHK1, as we had previously investigated its effect on the regulation of ERα levels and cell proliferation in different BC cell lines20) was more effective in reducing ERα levels in MCF-7, BT-474, and T47D-1 cell lines than in ZR-75-1, MDA-MB-361, EFM192C, and HCC1428 cells. This evidence concerns the gene PLK4 and breast cancer.