ERBB2 and ductal breast carcinoma in situ: Using a 3D culture system to assess luminal filling of DCIS acini as well as DCIS Cancer Stem Cell (CSC) activity, two DCIS cells lines, SUM225 (HER2−), and MCF10DCIS HER2 (HER2+), as well as human primary DCIS samples (HER2±) were studied.