ESR1 and breast cancer: Among the 918 patients with residual invasive BC, high ER levels (Allred score 6-8) were maintained at surgery after 6 months of NET in 97.2% (95% CI, 94.5%-98.2%) receiving anastrozole, 75.7% (95% CI, 70.4%-80.4%) receiving fulvestrant, and 71.3% (95% CI, 66.2%-76.1%) receiving A+F, an expected difference given the ER downregulation effect of fulvestrant.