ERBB2 and breast cancer: In a recent comprehensive analysis of 12 mouse mammary cancer cell lines (Yang et al., 2017), D2A1 cells are classified as oestrogen receptor (ER)- and ErbB2/HER2-negative, Pik3ca and Trp53 wild type, having a ‘claudin-low’ transcriptional profile and assignment to the luminal B subtype.