Further analysis showed that MCM3 was not significantly associated with RFS or breast cancer-specific death in the ER− patient subgroup in the STO-3 cohort (Fig. 3e, f) and similar observation was made in ER− patients obtained from the KM plotter data (data not shown), which suggests that the prognostic and predictive value of MCM3 is restricted to the ER+ breast cancer subgroup. This evidence concerns the gene ESR1 and breast cancer.