ESR1 and ductal breast carcinoma in situ: The ER+/PR+ human DCIS cell lines described here together with the mouse intraductal DCIS (MIND) xenograft model provide opportunities to advance studies and our understanding of how steroid hormone signaling pathways may be useful to identify biomarkers to better stratify DCIS patients for treatment options and for development of strategies for prevention of DCIS progression to invasive breast cancer.