Patients with ER+, IGF‐1R‐positive breast cancer without p‐IGF‐1R/InsR staining (n = 242) had tamoxifen benefit (HR 0.41, p = 0.0038), while the results for p‐IGF‐1R/InsR‐positive patients (n = 125) were not significant (HR 0.95, p = 0.3). This evidence concerns the gene ESR1 and breast cancer.