To examine the molecular mechanisms underlying CHIP-mediated ErbB2 degradation, we developed stable control and CHIP knockdown (KD) versions of ErbB2-overexpressing breast cancer cell lines SKBR3 and 21MT1 and used these along with their previously established vector control and Myc-tagged CHIP overexpressing transfectants [37]. This evidence concerns the gene ERBB2 and breast cancer.