The HT29 cells have mutant p53, while HCT116 cells have wild-type p53 (Jia et al, 1997; Violette et al, 2002) and although it has previously been suggested that the mechanisms of XR5944-mediated cell cycle arrest may be independent of p53 status (Sappal et al, 2003), the cell cycle response to both 5-FU and CPT-11 treatment in colon cancer cells has been reported to be influenced by p53 status (Magrini et al, 2002; Violette et al, 2002). This evidence concerns the gene TP53 and malignant colon neoplasm.