PAK1 and head and neck neoplasm: For example, both activity and expression of the serine/threonine kinase Pak1, an effector of the Rac and Cdc42 GTPases and potential cortactin accomplice, was found to be elevated in head and neck tumours as compared with adjacent normal tissue biopsy specimens (Yang et al, 2004), although this study was limited to a small number of tumours.