Both gene-expression-based ER classifications yielded higher hazard ratios in ER negative compared to ER positive tumours than IHC based ER status when assessing risk of disease recurrence (disease-free survival) (IHC based ER status HR = 1.84, 95% CI: 1.16–2.93, Figure 2a; ESR1 based: HR = 1.98, 95% CI: 1.26–3.12, Figure 2b; 23-gene ER signature based: HR = 2.31, 95% CI: 1.47–3.63, Figure 2c). Here, ESR1 is linked to neoplasm.