Fribbens and colleagues reported that the E380Q ESR1 mutation was found in 9.5% (6/63) in the SoFEA study for hormone receptor (HR)-positive BC patients who had demonstrated prior sensitivity to AIs, but it was found in 24.4% (22/91) in the PALOMA3 trial for HR–positive BC patients who had progressed during prior ET [19]. This evidence concerns the gene ESR1 and breast cancer.