ESR1 and breast carcinoma: Another study, which involved 9639 patients with primary breast carcinoma treated at The University of Texas MD Anderson Cancer Center from 1990 to 2011, demonstrated that, regardless of HER2 status, primary breast carcinoma patients with an ER expression of 1%–9% had similar recurrence-free survival (RFS) to those with an ER expression of < 1% (hazard ratio (HR) = 1.2, 95% confidence interval (CI) of HR = 0.9–1.7, p = 0.2), and both groups had significantly worse RFS than those with an ER expression of ≥ 10% [8].