This type of tumors was chosen because the MAPK is frequently overactivated in human HCC [31] and because previous studies by our group revealed that enzymes of cholesterol biosynthesis, namely Hmgcs1 (3-hydroxy-3-methylglutaryl-CoA synthase) and Lss (lanosterol synthase), are transcriptionally up-regulated in chemically induced mouse liver tumors with an activated Ras/Raf/MAPK pathway. The gene discussed is HMGCS1; the disease is hepatocellular carcinoma.