Zhou H, Li J, Chen Z, et al. - Whether and how nitric oxide (NO) is associated with lung cancer, was investigated via this meta-analysis. Relevant studies were found via comprehensive exploration in the databases. Overall 50 studies with 2551 cases and 1691 controls were analyzed. Much higher FeNO (fraction of exhaled nitric oxide) and blood NO levels were detected in lung cancer patients in comparison to that in controls. The highest blood NO level was observed in large cell carcinoma patients. FeNO and blood NO level did not differ significantly between pretreatment and posttreatment in all patients. However, NSCLC (non- small cell lung cancer) patients exhibited an increase in FeNO level and decline in blood NO level post-therapy. These findings indicate that FeNO and blood NO level would contribute to lung cancer diagnosis as well as assessment of treatment impact, particularly for NSCLC cases.