To address RA metabolism in HCC, we investigated three kinds of RA synthesis-related enzymes in HCC, including three alcohol dehydrogenases (ADH1, ADH2, ADH 3), two retinol dehydrogenases (RDH1, RDH10) and three retinaldehyde dehydrogenases (RALDH1, RALDH 2, RALDH 3) (Fig 1A). This evidence concerns the gene ALDH1A1 and hepatocellular carcinoma.