YAP1 and hepatocellular carcinoma: Conditional inactivation of Mst1/Mst2 in the liver results in the immediate onset of dramatic hepatocyte proliferation and hepatomegaly followed by the development of Hepatocellular carcinoma (HCC) and cholangiocarcinoma within 2 month, in which loss of Mst1/2-dependent inhibition of YAP contributes to the liver cell proliferation and tumorigenesis.