In addition to Pak4, other Pak family members are also overexpressed in breast cancer, particularly Pak1.14, 15, 16, 17, 18, 19, 20 Pak4 appears to be unique, however, in that wild-type Pak4 alone is sufficient to cause tumorigenesis in mice when overexpressed.4, 5. Here, PAK1 is linked to breast cancer.