number of in vitro studies have focused on the effect of the tumour suppressor gene p53 on expression of the MDR1 gene. These report an inhibitory role of the wild-type p53 on the MDR1 promoter region whereas mutant p53 variants act as activators, probably due to loss of its inhibitory role.83–86 Together with the T cell factor elements described earlier, these may represent only a relatively small contribution to the overall complex transcriptional regulation of the MDR1 gene by other transactivating genes. However, it has become apparent that the MDR1 gene may have an important role in the tumorigenesis of colorectal cancer