ESR1 and cancer: The subgroup of patients with ER/PR-negative cancers without amplification of TOP2A in particular had the worst RFS rates (HR = 0.29, 95% CI 0.13 to 0.65, P = 0.001) and the worst OS rates (HR = 0.28, 95% CI 0.10 to 0.76, P = 0.008).