A Kaplan-Meier analysis of the Pawitan set revealed that RRM2 mRNA levels, similar to uPA, which is a validated prognostic biomarker for ER-negative breast cancer[49], were significantly associated with poor OS and PFS in a dose-dependent manner in ER-negative, but not ER-positive, breast cancers (Additional file1: Figure S4). Here, ESR1 is linked to breast carcinoma.