ESR1 and breast cancer: Univariate analysis and Cox regression analyses revealed that postoperative N stage (p < 0.001), postoperative ER status (HR = 0.568 [95% CI 0.350–0.919]; p = 0.021), MP grade (p = 0.006), and targeted therapy (p = 0.003) were independent prognostic factors in patients with HER2‐positive breast cancer following NAT.