CDC42 and cancer: 1). By regulating the cellular architecture, Cdc42 also plays roles in cell motility, survival, and proliferation. Although the introduction of a Cdc42 mutant into fibroblasts showed hallmarks of transformation, activating mutations of Cdc42 have not been found in human cancers (2). Gene targeting, however, has demonstrated an essential role for Cdc42 downstream of Ras (3).