KMO and neoplasm: These results indicate that upregulation of KMO has a tumor‐promoting effect on HCC, and the mechanism may be that KMO affects the abnormal metabolism of kynurenine, leading to abnormal NAD concentration in HCC, resulting in NADH/NAD+ redox steady state destruction, thereby promoting the development of cancer, and so KMO can be used as a new prognostic marker for HCC.