DHODH and cancer: Figure 6b shows the specific activity of DHODH in malignant tumour and matched normal tissues (n = 5 each). The specific activity of DHODH in the malignant tumour tissue (1.10 ± 0.19 nmol/mg total proteins/h) was approximately 5 times higher than that in adjacent normal tissue (0.24 ± 0.11 nmol/mg total proteins/h). However, the concentration of endogenous orotic acid was similar in both malignant tumour (1.09 ± 0.16 nmol/mg total proteins) and adjacent normal (1.28 ± 0.19 nmol/mg total proteins) tissues (Fig. 6c).