ESR1 and breast cancer: Furthermore, Vallon-Christersson et al. compared stratification based on a wide range of gene signatures, using RNA sequencing profiles in a large population-based breast cancer cohort [21]; they found agreement between most signatures in the low- and high-risk groups for the ER+/HER− tumors, and less agreement within the intermediate-risk samples; this is consistent with our results, and stresses that there is a continuous need for improved risk predictors in this patient population.