In neoplastic tissue, PAKs, particularly PAK1, PAK2 and PAK4, have a high level of expression in many cancers with PAK alterations involving gene amplification, fusions, mutations and deletions resulting in PAKs playing key roles in pancreatic cancer [2,75,76,214,215], as well as in lung, colon, gastric, prostate and breast cancer [6,22,27]. Here, PAK4 is linked to breast cancer.