The potential clinical applicability of linsitinib has been studied in a variety of advanced cancer patients, but these trials failed to demonstrate antitumor activity.44, 45, 46 Our data suggest that the subset of high‐risk postmenopausal ER+ breast cancer patients characterized by PI3K/MAPK pathway activation via IGF‐1R may have more benefit from adjuvant tamoxifen to which linsitinib is added than from adjuvant tamoxifen alone. This evidence concerns the gene ESR1 and breast cancer.