Although DCIS grade, expression of the estrogen receptor (ER), human epidermal growth factor receptor 2 (HER2) and prostaglandin-endoperoxide synthase 2 (COX-2) have shown an association with invasive progression (10, 11, 12, 13), the clinical utility of their prognostic value is a subject of ongoing debate (9, 10, 11, 12, 13, 14, 15, 16, 17). Here, ESR1 is linked to ductal breast carcinoma in situ.