Human epidermal growth factor receptor 2 (ERBB2, formerly HER2/neu, c-erbB2), 1 of a family of 4 membrane tyrosine kinases (TKs), was found to be amplified in a human breast cancer cell line 26 years ago [21], and this amplification was shown to be important in the pathogenesis and progression of human breast cancer [22]. Here, CDC42 is linked to breast cancer.