Consistent with these findings, functional studies using transgenic mouse models have also demonstrated that overexpression of PAK1 in the mammary gland promotes the formation of preneoplastic lesions and breast tumors [17] and that PAK1 contributes to human endothelial growth factor receptor 2 (HER2)/Neu-driven tumorigenesis [18]. This evidence concerns the gene ERBB2 and breast neoplasm.