ESR1 and breast cancer: Approximately half (n = 37, 49.3%) of all patients had invasive estrogen receptor-positive (ER+) breast cancers, approximately one-third had invasive triple-negative breast cancers, with the remaining patients having ER-negative (ER−), human epidermal growth factor receptor 2-positive (HER2+) invasive breast cancers or ductal carcinoma in situ (DCIS).