ERBB2 and breast cancer: For the murine HER2-positive breast cancer cell line, the brain metastatic cells expressing avian erythroblastosis oncogene B2 (ErbB2) (ErbB2-BrM2) were established from MMTV-driven NeuNT transgenic murine mammary tumor cells by repetitive in vivo selection using the intracardiac injection method [93,96,115].