CAT and adenoma: It was found that the human colorectal tumors (adenomas and carcinomas) have increased levels of different markers of oxidative stress, such as increased levels of ROS (measured by chemiluminescence), nitric oxide (NO) [32], 8-oxodG in DNA [33], lipid peroxides, glutathione peroxidase (GPx), catalase (CAT) [34], and decreased methylation of cytosine in DNA [33].