Patient 1 had an estrogen receptor (ER)–positive, progesterone receptor (PR)–positive, HER2-positive (IHC score, 2+; FISH ratio, 2.0) right-breast invasive ductal carcinoma (IDC) diagnosed in 2016 and underwent mastectomy followed by adjuvant therapy. Here, ESR1 is linked to invasive ductal breast carcinoma.