Inhibitor of differentiation/DNA-binding 1 protein inhibitor (Id1), a liver-enriched factor, functions as a dominant negative inhibitor of basic helix-loop-helix (bHLH) transcription factors by blocking their binding to promoter DNA, and is highly expressed in HBV-related hepatocellular carcinoma (HCC) tumor tissues 15,16. The gene discussed is ID1; the disease is hepatocellular carcinoma.