Immunohistochemistry staining of xenograft tumours showed that p21WAF1/CIP1 expression was remarkably higher in PXR-HT29 tumours than in Vector-HT29 tumours (Figure 6A and C), but p53 expression appeared to be the same in the two groups most likely due to p53 mutation in HT29 cells. This evidence concerns the gene CDKN1A and neoplasm.