Metformin reduced CD133 expression in the HCC cell lines HepG2, JHH6, JHH7, and Huh1, and these effects were associated with the adenosine monophosphate (AMP)-activated protein kinase (AMPK)/CCAAT/enhancer-binding protein beta (CEBPβ) signaling pathway. The gene discussed is PROM1; the disease is hepatocellular carcinoma.