SMAD6 and hepatocellular carcinoma: A significant decrease in the p‐Smad1/5/8 and Smad6 levels following the increase in the p‐Smad3 level was detected in the HUVECs pre‐incubated with HBV‐infected hepatoma cells compared with those pre‐incubated with HBV‐uninfected hepatoma cells.