As no constitutively active mutant forms of Rho GTPases have been found in human tumors [4] and overexpression of Rho GTPases such as Rac1 and Cdc42 occurs in many malignancies including prostate cancer [7], [35], [36], [37], it can be assumed that over-expression rather than Rho GTPase activation mutations is associated with tumorigenesis. Here, CDC42 is linked to prostate cancer.