The development of Cdc42 inhibitors suitable for use in the clinic could prove of considerable therapeutic value, as levels of Cdc42 in breast tumour lysates exceed by as much as 50-fold those seen in normal tissue from the same patients and elevated levels of Cdc42 also have been observed in lung cancer and in colorectal cancer (Fritz et al, 1999, 2002). This evidence concerns the gene CDC42 and lung cancer.