The tissue distribution varies among different forms, with Rac1 ubiquitously expressed in most tissues, Rac2 mainly in hematopoietic cells, Rac3 highly enriched in the brain but expressed in other tissues as well at lower levels and the splice variant Rac1b minimally expressed in normal cells but highly enriched in cancers such as breast and colorectal cancers (Haataja et al., 1997; Jordan et al., 1999; Schnelzer et al., 2000; Chan et al., 2005). This evidence concerns the gene RAC1 and cancer.