Estrogen receptor (ER) signaling regulates the survival and growth of mammary epithelial cells2 and is altered in premalignant breast lesions such as atypical ductal hyperplasia (ADH) and ductal carcinoma in situ (DCIS), as well as in invasive ductal cell carcinoma (IDC)3,4. Here, ESR1 is linked to ductal breast carcinoma in situ.