It was initially unexpected to observe that metformin upregulates H19 expression both in mouse fetal livers (Figure 2a) and in human Huh7 hepatoma cells (Figure 3d), given that metformin inhibits H19 expression in human endometrial and ovarian cancer cells.16, 36 Metformin has also long been known to repress gluconeogenesis in the adult liver.37 However, this apparent contradiction could be explained by cell/tissue-dependent and developmental stage-dependent effects of metformin. Here, H19 is linked to hepatocellular carcinoma.