It has been shown that PAK1 gene is frequently amplified in human breast cancer; PAK1 amplification is associated with resistance to tamoxifen; transgenic expression of an activated PAK1 allele induces transformation of mammary epithelial cells in culture and induces breast cancer in mice; and expression of dominant-negative alleles, shRNAs, or treatment with PAK inhibitors, impede the growth and/or normalize the morphology of various breast cancer cell lines in tissue culture [28-32]. Here, PAK1 is linked to breast cancer.