ESR1 and breast cancer: The ExteNET trial [27], which evaluated the benefit of neratinib vs placebo after trastuzumab-based adjuvant therapy in HER2-positive breast cancer, reported statistically significant fewer invasive disease-free survival (iDFS) events in the neratinib group (HR 0.73, 95% CI 0.57–0.92, P = 0.0083), which was the most significant in the ER+ patients.