ESR1 and breast cancer: Kaplan–Meier curves were retrieved by the Kaplan–Meier Plotter database (https://kmplot.com/analysis/) [27] and showed that women with ERα-negative BC (Fig. 1E, G and Supplementary Table 3) display an increased relapse-free survival (RFS) rate when the tumor expresses high levels of either CHK1 or CHK2 while, on the contrary, women with ERα-positive BCs expressing low levels of either CHK1 or CHK2 have a high RFS probability with respect to those patients expressing high CHK1 and CHK2 mRNA levels (Fig. 1F, H and Supplementary Table 3).