ERBB2 and breast neoplasm: FACS studies on live, non-permeabilized, unfixed cells were performed to compare cell surface binding of anti-HER2 antibodies to MAb 2009 on cells expressing human HER2 (HER2-amplified human breast carcinoma line SK-BR-3), rat neu (rat fibroblasts DHFR-G8; rat breast tumor cells LA7 and RBA), and mouse neu (4T1 and EMT6 mouse breast tumor cells; HC11 mouse mammary epithelial cells).