ESR1 and invasive ductal breast carcinoma: On pathological examination, the tumor consisted of a 1-mm micro-invasive ductal carcinoma (IDC) with 5 cm of intra-ductal component, and surgical margins were negative (Fig. 1a, right panel); the tumor was positive for estrogen receptor (ER) and progesterone receptor (PgR) and negative for human epidermal growth factor 2 (HER2) and lymphatic vessel invasion, with a nuclear grade (NG) score of 2 and Ki67 of 10 %.