Background: Cancer has the highest disease-related mortality rate in Iran. Reduced activity of paraoxonase reported in patients with cancer may be due to a reduction in its antioxidant properties and a subsequent increased risk of developing cancer. We aimed to assess antioxidant and oxidative status in patients with cancer through measuring the activity of PON1 as an antioxidant enzyme and determining MDA as a marker of oxidative stress. 
Methods: This case-control study was conducted on 50 patients with colon, lung, blood or breast cancer and 50 age- and sex-matched healthy controls matching during 2014-2015. Paraoxonase-1 and arylesterase activities were measured with paraoxon and phenylacetate substrates and their malondialdehyde levels and serum lipid profile were determined through spectrophotometry.
Results: Serum paraoxonase activity was lower in patients with cancer (28.52±2.77 IU/L) compared with the healthy subjects (96.57±1.49 IU/L; P<0.0001). Similarly, serum arylesterase activity was lower in patients with cancer (49.27±2.90) than the controls (66.91±2.47; P<0.0001). MDA levels were higher in patients with cancer (1.3166±0.0876) than the healthy controls (0.9008±0.0452). The Mann-Whitney U-Test showed significant differences between the two groups in terms of their triglyceride levels (P<0.05). Although serum HDL levels were higher in the control group compared with the cases, the difference was not statistically significant (P>0.05). Serum VLDL, LDL and total cholesterol levels differed significantly between the two groups (P<0.05).
Conclusion: The results obtained showed a reduction in paraoxonase activity and an increased lipid oxidation in the patients with cancer and thereby reduced the antioxidant power of paraoxonase and weakened the body’s antioxidant system.