ERBB2 and breast cancer: To further test this idea, nine breast cancer cell lines and two non-tumorigenic breast epithelial cell strains with different growth rates (Figure S2) and with varying ER, p53 and HER2/neu status (Table 1) were infected with GFP, GFP-ING1b or GFP-ING2 to see if ING proteins affected breast cancer cells in a p53-sensitive or growth rate-dependent manner.