Previous clinical studies also found an overexpression of DPD in tumour cells to be associated with 5-FU resistance (Higashiyama et al, 2001) and a poor prognosis in many cancer patients treated with 5-FU, including NSCLCs (Huang et al, 2000; Nakagawa et al, 2002), colorectal cancers (Ichikawa et al, 2003b), and breast cancers (Horiguchi et al, 2004). This evidence concerns the gene DPYD and cancer.