ESR1 and breast carcinoma: 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.